puberty
   HOME

TheInfoList



OR:

Puberty is the process of physical changes through which a
child A child (: children) is a human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedality, bipedalism and exceptional cognitive skills due to a large and complex Human brain, brain ...
's body matures into an
adult An adult is a human or other animal that has reached Developmental biology, full growth. In human context, the term ''adult'' has meanings associated with social and Law, legal concepts. In contrast to a "Minor (law), minor", a legal adult is a p ...
body capable of
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex Biological life cycle, life cycle in which a gamete (haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to p ...
. It is initiated by hormonal signals from the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
to the
gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland that produces the Gamete, gametes and Sex hormone, sex hormones of an organism. Female reproductive cells are Egg cell, egg cells, and male reproductive cells are sp ...
s: the ovaries in a girl, the
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
in a boy. In response to the signals, the gonads produce hormones that stimulate
libido Libido (; colloquial: sex drive) is a person's overall sexual drive or desire for Human sexual activity, sexual activity. Libido is influenced by biological, psychological, and social factors. Biologically, the sex hormones and associated neurotr ...
and the growth, function, and transformation of the brain,
bone A bone is a rigid organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic ...
s,
muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...
,
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells, and transports Metabolic waste, metabolic waste products away from th ...
,
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
,
hair Hair is a protein filament that grows from hair follicle, follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick ter ...
,
breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryology, embryological tissues. In females, it serves as the mammary gland, which produce ...
s, and
sex organ A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
s. Physical growth—height and weight—accelerates in the first half of puberty and is completed when an adult body has been developed. Before puberty, the external sex organs, known as primary sexual characteristics, are sex characteristics that distinguish boys and girls. Puberty leads to
sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different Morphology (biology), morphological characteristics, particularly characteristics not directly involved in reproduction. The conditio ...
through the development of the secondary sex characteristics, which further distinguish the sexes. On average, girls begin puberty at ages 10–11 and complete puberty at ages 15–17; boys generally begin puberty at ages 11–12 and complete puberty at ages 16–17. The major landmark of puberty for females is
menarche Menarche ( ; ) is the first menstrual cycle, or first Menstruation, menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of f ...
, the onset of menstruation, which occurs on average between ages 12 and 13. For males, first
ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the Male reproductive system, male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, a ...
,
spermarche Spermarche—also known as semenarche—is the beginning of development of sperm in boys' testicles at puberty.''Adolescence and Emerging Adulthood: A Cultural Approach'', Jeffrey Jensen Arnett, N.J.: Prentice-Hall, 3rd edition, 2006. It is the c ...
, occurs on average at age 13. In the 21st century, the average age at which children, especially girls, reach specific markers of puberty is lower compared to the 19th century, when it was 15 for girls and 17 for boys (with age at first periods for girls and voices break for boys being used as examples). This can be due to any number of factors, including improved nutrition resulting in rapid body growth, increased weight and fat deposition, or exposure to
endocrine disruptor Endocrine disruptors, sometimes also referred to as hormonally active agents, endocrine disrupting chemicals, or endocrine disrupting compounds are chemicals that can interfere with endocrine (or Hormone, hormonal) systems. These disruptions can ...
s such as
xenoestrogen Xenoestrogens are a type of xenohormone that imitates estrogen. They can be either synthetic or natural chemical compounds. Synthetic xenoestrogens include some widely used industrial compounds, such as Polychlorinated biphenyls, PCBs, Bisphenol A ...
s, which can at times be due to food consumption or other environmental factors. However, more modern archeological research suggests that the rate of puberty as it occurs now is the intended way. Growth spurts began at around 10–12, but markers of later stages of puberty such as menarche had delays that correlated with severe environmental conditions such as poverty, poor nutrition, air and pollution. Puberty that starts earlier than usual is known as
precocious puberty In medicine, precocious puberty is puberty occurring at an unusually early age. In most cases, the process is normal in every aspect except the unusually early age and simply represents a human variability, variation of Human development (biology ...
, and puberty which starts later than usual is known as delayed puberty. Notable among the morphologic changes in size, shape, composition, and functioning of the pubertal body, is the development of secondary sex characteristics, the "filling in" of the child's body; from girl to woman, from boy to man. Derived from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
' (age of maturity), the word ''puberty'' describes the physical changes to sexual maturation, not the
psychosocial The psychosocial approach looks at individuals in the context of the combined influence that psychological factors and the surrounding social environment have on their physical and mental wellness and their ability to function. This approach is ...
and cultural maturation denoted by the term ''adolescent development'' in
Western culture image:Da Vinci Vitruve Luc Viatour.jpg, Leonardo da Vinci's ''Vitruvian Man''. Based on the correlations of ideal Body proportions, human proportions with geometry described by the ancient Roman architect Vitruvius in Book III of his treatise '' ...
, wherein
adolescence Adolescence () is a transitional stage of physical and psychological development that generally occurs during the period from puberty to adulthood (typically corresponding to the age of majority). Adolescence is usually associated with th ...
is the period of mental transition from childhood to
adult An adult is a human or other animal that has reached Developmental biology, full growth. In human context, the term ''adult'' has meanings associated with social and Law, legal concepts. In contrast to a "Minor (law), minor", a legal adult is a p ...
hood, which overlaps much of the body's period of puberty.


Differences between male and female puberty

Two of the most significant differences between puberty in girls and puberty in boys are the age at which it begins, and the major
sex steroid Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are ...
s involved, the
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This i ...
s and the
estrogen Estrogen or oestrogen is a category of sex steroid, sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogeny (biology), endogenous estrogens th ...
s. Although there is a wide range of normal ages, girls typically begin puberty around ages 10–11 and end puberty around 15–17; boys begin around ages 11–12 and end around 16–17. Girls attain reproductive maturity about four years after the first physical changes of puberty appear. In contrast, boys accelerate more slowly but continue to grow for about six years after the first visible pubertal changes.Garn, SM. Physical growth and development. In: Friedman SB, Fisher M, Schonberg SK., editors. Comprehensive Adolescent Health Care. St Louis: Quality Medical Publishing; 1992. Retrieved on 2009-02-20 Any increase in height beyond the post-pubertal age is uncommon. For boys, the
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This i ...
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate The prostate is both an Male accessory gland ...
is the principal
sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are ...
; while testosterone is produced, all boys' changes are characterized as
virilization Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens. Virilization is most commonly used in three medical and Biologic ...
. A substantial product of testosterone metabolism in males is the
estrogen Estrogen or oestrogen is a category of sex steroid, sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogeny (biology), endogenous estrogens th ...
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous cycle, estrous and menstrual cycle, menstrual female reproductive cycles. Estradiol is resp ...
. The conversion of testosterone to estradiol depends on the amount of body fat and estradiol levels in boys are typically much lower than in girls. The male "growth spurt" also begins later, accelerates more slowly, and lasts longer before the
epiphyses The epiphysis () is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the join ...
fuse. Although boys are on average shorter than girls before puberty begins, adult men are on average about taller than women. Most of this sex difference in adult heights is attributable to a later onset of the growth spurt and a slower progression to completion, a direct result of the later rise and lower adult male levels of estradiol. The hormonal maturation of females is considerably more complicated than in males. The main
steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the adrenal cortex, hence ''cortico-'') and sex steroids (typically made in the gonads or placenta). Withi ...
s, testosterone, estradiol, and
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major ...
as well as
prolactin Prolactin (PRL), also known as lactotropin, is a protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions w ...
play important physiological functions in puberty. The production of gonadal steroids in girls starts with production of testosterone, which is typically quickly converted to estradiol inside the ovaries. However the rate of conversion from testosterone to estradiol (driven by FSH/LH balance) during early puberty is highly individual, resulting in very diverse development patterns of
secondary sexual characteristics Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These characteristics are particularly evident in the sexual dimorphism, sexually dimorphic phenotypic traits that distinguis ...
. Production of progesterone in the ovaries begins with the development of ovulatory cycles in girls (during the lutheal phase of the cycle), before puberty low levels of progesterone are produced in the adrenal glands of both boys and girls. Estradiol levels rise earlier and reach higher levels in women than in men. While estradiol promotes growth of the breasts and
uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around p ...
, it is also the principal hormone driving the pubertal growth spurt and epiphyseal maturation and closure.


Puberty onset

Puberty is preceded by
adrenarche Adrenarche is an early stage in sexual maturation that happens in some higher primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and ...
, marking an increase of adrenal androgen production between ages 6–10. Adrenarche is sometimes accompanied by the early appearance of axillary and pubic hair. The first androgenic hair resulting from adrenarche can be also transient and disappear before the onset of true puberty. The onset of puberty is associated with high
GnRH Gonadotropin-releasing hormone (GnRH) is a releasing hormone Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are a ...
pulsing, which precedes the rise in sex hormones, LH and FSH. Exogenous GnRH pulses cause the onset of puberty. Brain tumors which increase GnRH output may also lead to premature puberty. The cause of the GnRH rise is unknown.
Leptin Leptin (from Ancient Greek, Greek λεπτός ''leptos'', "thin" or "light" or "small") is a hormone predominantly made by adipose cells and enterocytes in the small intestine that helps to regulate Energy homeostasis, energy balance by inhib ...
might be the cause of the GnRH rise. Leptin has receptors in the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
which synthesizes GnRH. Individuals who are deficient in leptin fail to initiate puberty. The levels of leptin increase with the onset of puberty, and then decline to adult levels when puberty is completed. The rise in GnRH might also be caused by genetics. A study discovered that a mutation in genes encoding both neurokinin B as well as the neurokinin B receptor can alter the timing of puberty. The researchers hypothesized that neurokinin B might play a role in regulating the secretion of kisspeptin, a compound responsible for triggering direct release of GnRH as well as indirect release of LH and FSH.


Effects of early and late puberty onset

Several studies about puberty have examined the effects of an early or a late onset of puberty in males and females. In general, girls who enter puberty late experience positive outcomes in adolescence and adulthood, while girls who enter puberty early experience negative outcomes. Boys who have earlier pubertal timing generally have more positive outcomes in adulthood but more negative outcomes in adolescence, while the reverse is true for later pubertal timing.


Girls

Outcomes have generally indicated that early onset of puberty in girls can be psychologically damaging. The main reason for this detrimental effect is the issue of
body image Body image is a person's thoughts, feelings and perception of the aesthetics or sexual attractiveness of their own body. The concept of body image is used in a number of disciplines, including neuroscience, psychology, medicine, psychiatry, psy ...
. As they physically develop, gaining weight in several areas of the body, early-maturing girls usually look larger than girls who have not yet entered puberty. A result of the social pressure to be thin, the early-maturing girls develop a negative view of their body image. In addition, people may tease the girls about their visible breasts, forcing the early-maturing girl to hide her breasts by dressing differently. Embarrassment about a more developed body may also result in the refusal to undress for gym. These experiences lead to lower self-esteem, more depression and poorer body image in these early-maturing girls. Furthermore, as physical and emotional differences set them apart from people in their same age group, early-maturing girls develop relationships with older people. For instance, some early-maturing girls have older boyfriends, "attracted to the girls' womanly physique and girlish innocence." While having an older boyfriend might improve popularity among peers, it also increases the risk of alcohol and drug use, increased sexual relations (often unprotected), eating disorders and bullying. Generally, later onset of puberty in girls produces positive outcomes. They exhibit positive behaviors in adolescence that continue to adulthood.


Boys

In the past, early onset of puberty in boys has been associated with positive outcomes, such as leadership in high school and success in adulthood. However, recent studies have revealed that the risks and problems of early maturation in males might outweigh the benefits. Early-maturing boys develop "more aggressive, law-breaking, and alcohol abusing" behaviors, which result in anger towards parents and trouble in school and with the police. Early puberty also correlates with increased sexual activity and a higher instance of teenage pregnancy, both of which can lead to depression and other psychosocial issues. However, early puberty might also result in positive outcomes, such as popularity among peers, higher self-esteem and confidence, as a result of physical developments, such as taller height, developed muscles, muscular male breast and better athletic ability. On the other hand, late-maturing boys develop lower self-esteem and confidence and generally have lower popularity among peers, due to their less-developed physiques. Also, they experience problems with anxiety and depression and are more likely to be afraid of sex than other boys.


Changes in males

In boys, puberty begins with the enlargement of the testicles and scrotum. The penis also increases in size, and a boy develops pubic hair. A boy's testicles also begin making
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as ...
. The release of
semen Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoon, spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphrodite, hermaphroditic animals and can fertili ...
, which contains sperm and other fluids, is called
ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the Male reproductive system, male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, a ...
. During puberty, a boy's erect penis becomes capable of ejaculating semen and impregnating a female. A boy's first ejaculation is an important milestone in his development. On average, a boy's first ejaculation occurs at age 13. Ejaculation sometimes occurs during sleep; this phenomenon is known as a
nocturnal emission A nocturnal emission, informally known as a wet dream, sex dream, nightfall or sleep orgasm, is a spontaneous orgasm during sleep that includes ejaculation for a male, or vaginal lubrication, vaginal wetness or an orgasm (or both) for a female. ...
.


Testicular size

In boys, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarche).
Testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
in prepubertal boys change little in size from about 1 year of age to the onset of puberty, averaging about 2–3 cm in length and about 1.5–2 cm in width. The size of the testicles is among the parameters of the Tanner scale for male genitals, from stage I which represents a volume of less than 1.5 ml, to stage V which represents a testicular volume of greater than 20 ml. Testicular size reaches maximal adult size about 6 years after the onset of puberty. While 18–20 cm3 is an average adult size, there is wide variation in testicular size in the normal population. After the boy's testicles have enlarged and developed for about one year, the length and then the breadth of the shaft of the
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during Copulation (zoology), copulation. Such organs occur in many animals, both #Vertebrates, vertebra ...
will increase and the
glans penis In male Male (Mars symbol, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot sexual repr ...
and corpora cavernosa will also start to enlarge to adult proportions.


Male musculature and body shape

By the end of puberty, adult men have heavier
bone A bone is a rigid organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic ...
s and nearly twice as much skeletal
muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...
. Some of the bone growth (e.g. shoulder width and jaw) is disproportionately greater, resulting in noticeably different male and female skeletal shapes. The average adult male has about 150% of the lean body mass of an average female, and about 50% of the body fat. This muscle develops mainly during the later stages of puberty, and muscle growth can continue even after boys are biologically adult. The peak of the so-called "strength spurt", the rate of muscle growth, is attained about one year after a male experiences his peak growth rate. Often, the fat pads of the male breast tissue and the male nipples will develop during puberty; sometimes, especially in one breast, this becomes more apparent and is termed
gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of Breast#Anatomy, breast tissue as a result of a endocrine disorder, hormone imbalance between estrogens and ...
. It is usually not a permanent phenomenon.


Erections

Erection An erection (clinically: penile erection or penile tumescence) is a Physiology, physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, ...
s during sleep or when waking up are medically known as nocturnal penile tumescence and colloquially referred to as ''morning wood''. The penis can regularly get erect during sleep and men or boys often wake up with an erection. Once a boy reaches his
teenage Adolescence () is a transitional stage of Developmental biology, physical and psychological Human development (biology), development that generally occurs during the period from puberty to adulthood (typically corresponding to the age of majo ...
years, erections occur much more frequently due to puberty. Erections can occur spontaneously at any time of day, and if clothed may cause a bulge or "hump". This can be disguised or hidden by wearing close-fitting underwear, a long shirt and baggier clothes. Erections are common for male prepubescent children and infants, and can even occur before birth. Spontaneous erections are also known as involuntary or unwanted erections and are normal. Such erections can be embarrassing if they happen in public, such as a classroom or living room.


Foreskin retraction

During puberty, if not before, the tip and opening of a boy's
foreskin In male Human body, human anatomy, the foreskin, also known as the prepuce, is the double-layered fold of skin, Mucous membrane, mucosal and Muscle tissue, muscular tissue at the distal end of the human penis that covers the glans penis, glans a ...
becomes wider, progressively allowing for retraction down the shaft of the
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during Copulation (zoology), copulation. Such organs occur in many animals, both #Vertebrates, vertebra ...
and behind the
glans The glans (, plural "glandes" ; from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then k ...
, which ultimately should be possible without pain or difficulty. The membrane that bonds the inner surface of the foreskin with the glans disintegrates and releases the foreskin to separate from the glans. The foreskin then gradually becomes retractable. Research by Øster (1968) found that with the onset and continuation of puberty, the proportion of boys able to pull back their foreskins increased. At ages 12–13, Øster found that only 60% of boys were able to retract their foreskins; this increased to 85% by ages 14–15, and 95% by 16–17. He also found that 1% of those unable to fully retract experienced
phimosis Phimosis (from Greek language, Greek φίμωσις ''phimōsis'' 'muzzling'.) is a condition in which the foreskin of the Human penis, penis cannot stretch to allow it to be pulled back past the Glans penis, glans. A balloon-like swelling under ...
at ages 14–17, the remainder were partially able to. The findings were supported by further research by Kayaba ''et al'' (1996) on a sample of over 600 boys, and Ishikawa and Kawakita (2004) found that by age 15, 77% of their sample of boys could retract their foreskins. Beaugé (1997) reports that boys may assist the development of retractile foreskin by manual stretching. Once a boy is able to retract his foreskin, penile hygiene should become an important feature of his routine body care. Although the
American Academy of Pediatrics The American Academy of Pediatrics (AAP) is an American professional association of pediatricians, headquartered in Itasca, Illinois. It maintains its Department of Federal Affairs office in Washington, D.C. Background The Academy was founded ...
states there is "little evidence to affirm the association between circumcision status and optimal penile hygiene", various studies suggest that boys be educated about the role of hygiene, including retracting the foreskin while urinating and rinsing under it and around the glans at each bathing opportunity. Regular washing under the foreskin was found by Krueger and Osborn (1986) to reduce the risk of numerous penile disorders, however Birley et al. (1993) report excessive washing with soap should be avoided because it dries the oils out of the tissues and can cause non-specific
dermatitis Dermatitis is inflammation of the Human skin, skin, typically characterized by itchiness, erythema, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become lichenification, thick ...
.


Pubic hair

Pubic hair Pubic hair is terminal hair, terminal body hair that is found in the sex organ, genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic reg ...
often appears on a boy shortly after the genitalia begin to grow. The pubic hairs are usually first visible at the dorsal (abdominal) base of the penis. The first few hairs are described as stage 2. Stage 3 is usually reached within another 6–12 months, when the hairs are too many to count. By stage 4, the pubic hairs densely fill the "pubic triangle". Stage 5 refers to the spread of pubic hair to the
thigh In Outline of human anatomy, human anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the Human leg, lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong ...
s and upward towards the
navel The navel (clinically known as the umbilicus, commonly known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All Placentalia, placental mammals have a nav ...
as part of the developing
abdominal hair Abdominal hair is the hair Hair is a protein filament that grows from hair follicle, follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in foll ...
.


Body and facial hair

In the months and years following the appearance of pubic hair, other areas of skin that respond to androgens may develop
androgenic hair Body hair, or androgenic hair, is the terminal hair In humans, terminal hair is a variant of hair that is thick and long such as what grows on the scalp, as compared with vellus hair, colloquially known as peach fuzz, growing elsewhere. ...
. The usual sequence is:
underarm The axilla (also, armpit, underarm or oxter) is the area on the human body The human body is the structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tiss ...
(axillary) hair, perianal hair, upper lip hair, sideburn (preauricular) hair, periareolar hair, and the
beard A beard is the hair that grows on the jaw, chin, upper lip, lower lip, cheeks, and neck of humans and some non-human animals. In humans, usually pubescent or adult males are able to grow beards. Throughout the course of history, societal at ...
area. As with most human biological processes, this specific order may vary among some individuals. Arm, leg,
chest The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main Tagma (biology), divis ...
,
abdominal The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
, and back hair become heavier more gradually. There is a large range in amount of body hair among adult men, and significant differences in timing and quantity of hair growth among different racial groups. Facial hair is often present in late adolescence, but may not appear until significantly later. Facial hair will continue to get coarser, darker and thicker for another 2–4 years after puberty. Some men do not develop full facial hair for up to 10 years after the completion of puberty. Chest hair may appear during puberty or years after, though not all men develop it.


Voice change and Adam's apple

Under the influence of androgens, the
larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...
(or voice box) grows in both sexes. This growth is far more prominent in boys, causing the male voice to drop and deepen, sometimes abruptly but rarely "overnight", about one
octave In music, an octave ( la, octavus: eighth) or perfect octave (sometimes called the Pythagorean interval, diapason) is the interval (music), interval between one musical Pitch (music), pitch and another with double its frequency. The octave rela ...
, because the longer and thicker
vocal folds In humans, vocal cords, also known as vocal folds or voice reeds, are folds of throat tissues that are key in creating sounds through vocalization. The size of vocal cords affects the pitch of voice. Open when breathing and vibrating for speech ...
have a lower
fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'', is defined as the lowest frequency of a Periodic signal, periodic waveform. In music, the fundamental is the musical pitch (music), pitch of a note that is perceived as ...
. Before puberty, the larynx of boys and girls is about equally small. Occasionally, voice change is accompanied by unsteadiness of vocalization in the early stages of untrained voices. Most of the voice change happens during stage 3–4 of male puberty around the time of peak growth. Adult pitch is attained at an average age of 15 years, although the voice may not fully settle until early twenties. It usually precedes the development of significant facial hair by several months to years.


Changes in females


Breast development

The first physical sign of puberty in girls is usually a firm, tender lump under the center of the
areola The human areola (''areola mammae'', or ) is the pigmented area on the breast around the nipple. Areola, more generally, is a small circular area on the Human body, body with a different histology from the surrounding Tissue (biology), tissu ...
of one or both
breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryology, embryological tissues. In females, it serves as the mammary gland, which produce ...
s, occurring on average at about 10.5 years of age. This is referred to as
thelarche Thelarche, also known as breast budding, is the onset of secondary breast development, often representing the beginning of pubertal development. It is the stage at which male and female breasts differentiate due to variance in hormone levels; howe ...
. By the widely used Tanner staging of puberty, this is stage 2 of breast development (stage 1 is a flat, prepubertal breast). Within 6–12 months, the swelling has clearly begun in both sides, softened, and can be felt and seen extending beyond the edges of the areolae. This is stage 3 of breast development. By another 12 months (stage 4), the breasts are approaching mature size and shape, with areolae and
nipple The nipple is a raised region of tissue on the surface of the breast from which, in females, breast milk, milk leaves the breast through the lactiferous ducts to feed an infant. The milk can flow through the nipple passively or it can be ejected ...
s forming a secondary mound. In most young women, this mound disappears into the contour of the mature breast (stage 5), although there is so much variation in sizes and shapes of adult breasts that stages 4 and 5 are not always separately identifiable.


Pubic hair

Pubic hair Pubic hair is terminal hair, terminal body hair that is found in the sex organ, genital area of adolescent and adult humans. The hair is located on and around the sex organs and sometimes at the top of the inside of the thighs. In the pubic reg ...
is often the second noticeable change in puberty, usually within a few months of thelarche. It is referred to as pubarche. The pubic hairs are usually visible first along the
labia The labia are part of the female genitalia; they are the major externally visible portions of the vulva. In humans, there are two pairs of labia: the ''labia majora'' (or the outer labia) are larger and thicker, while the ''labia minora'' are fol ...
. The first few hairs are described as Tanner stage 2. Stage 3 is usually reached within another 6–12 months, when the hairs are too numerous to count and appear on the pubic mound as well. By stage 4, the pubic hairs densely fill the "pubic triangle". Stage 5 refers to spread of pubic hair to the
thigh In Outline of human anatomy, human anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the Human leg, lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong ...
s and sometimes as
abdominal hair Abdominal hair is the hair Hair is a protein filament that grows from hair follicle, follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in foll ...
upward towards the
navel The navel (clinically known as the umbilicus, commonly known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All Placentalia, placental mammals have a nav ...
. In about 15% of girls, the earliest pubic hair appears before breast development begins.


Vagina, uterus, ovaries

Perineal skin
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers ...
izes due to effect of estrogen increasing its resistance to infection. The
mucosal A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of Epithelium, epithelial cells overlying a layer o ...
surface A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of Visual perception, sight ...
of the vagina also changes in response to increasing levels of
estrogen Estrogen or oestrogen is a category of sex steroid, sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogeny (biology), endogenous estrogens th ...
, becoming thicker and duller pink in color (in contrast to the brighter red of the prepubertal vaginal mucosa). Mucosa changes into a multilayered structure with superficial layer of squamous cells. Estrogen increase glycogen content in
vaginal epithelium The vaginal epithelium is the inner lining of the vagina consisting of multiple layers of ( squamous) cells. The basal membrane provides the support for the first layer of the epithelium-the basal layer. The intermediate layers lie upon the bas ...
, which in future plays important part in maintaining vaginal pH. Whitish secretions (physiologic
leukorrhea Leukorrhea or (leucorrhoea British English British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, " English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to t ...
) are a normal effect of estrogen as well. In the two years following thelarche, the
uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around p ...
, ovaries, and the follicles in the ovaries increase in size. The ovaries usually contain small follicular
cyst A cyst is a closed sac, having a distinct envelope and cell division, division compared with the nearby Biological tissue, tissue. Hence, it is a cluster of Cell (biology), cells that have grouped together to form a sac (like the manner in which ...
s visible by
ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...
. Before puberty, uterine body to cervix ratio is 1:1; which increases to 2:1 or 3:1 after completion of pubertal period.


Menstruation and fertility

The first menstrual bleeding is referred to as
menarche Menarche ( ; ) is the first menstrual cycle, or first Menstruation, menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of f ...
, and typically occurs about two years after
thelarche Thelarche, also known as breast budding, is the onset of secondary breast development, often representing the beginning of pubertal development. It is the stage at which male and female breasts differentiate due to variance in hormone levels; howe ...
. The average age of menarche is 12.5 in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. Most American girls experience their first period at 11, 12 or 13, but some experience it earlier than their 11th birthday and others after their 14th birthday. In fact, anytime between 8 and 16 is normal. In
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world ...
, the average age of menarche is 12.72, and in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
it is 12.9. The time between menstrual periods (menses) is not always regular in the first two years after menarche.
Ovulation Ovulation is the release of egg cells, eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be ...
is necessary for
fertility Fertility is the capability to produce offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual reproduction, two organisms. Collective ...
, but may or may not accompany the earliest menses. In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after menarche, 50% in the third year and 10% in the sixth year. Initiation of ovulation after menarche is not inevitable. A high proportion of girls with continued irregularity in the menstrual cycle several years from menarche will continue to have prolonged irregularity and anovulation, and are at higher risk for reduced fertility.


Body shape, fat distribution, and body composition

During this period, also in response to rising levels of estrogen, the lower half of the
pelvis The pelvis (plural pelves or pelvises) is the lower part of the Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pel ...
and thus
hips In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...
widen (providing a larger
birth canal In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the Vulval vestibule, vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucous membrane ...
). Fat tissue increases to a greater percentage of the body composition than in males, especially in the typical female distribution of breasts, hips, buttocks, thighs, upper arms, and pubis. Progressive differences in fat distribution as well as sex differences in local skeletal growth contribute to the typical female body shape by the end of puberty. On average, at 10 years, girls have 6% more body fat than boys.


Body odor and acne

Rising levels of
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This i ...
s can change the
fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an B ...
composition of
perspiration Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and Apocrine sweat gland, apocrine glands. The eccrine swea ...
, resulting in a more "adult"
body odor Body odor or body odour (BO) is present in all animals and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis, but can also be strongly influenced by various diseases ...
. This often precedes thelarche and pubarche by one or more years. Another androgen effect is increased secretion of oil (
sebum A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called #Sebum, sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greates ...
) from the skin. This change increases the susceptibility to
acne Acne, also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, black ...
, a skin condition that is characteristic of puberty. Acne varies greatly in its severity.


Visual and other effects of hormonal changes

In girls,
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous cycle, estrous and menstrual cycle, menstrual female reproductive cycles. Estradiol is resp ...
(the primary female sex hormone) causes thickening of lips and
oral mucosa The oral mucosa is the mucous membrane lining the inside of the mouth. It comprises stratified squamous epithelium, termed "oral epithelium", and an underlying connective tissue termed ''lamina propria''. The oral cavity has sometimes been describ ...
as well as further development of the
vulva The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external sex organ, female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, bulb of vestibu ...
. In the vulva and vagina, estradiol causes thickening ( stratification) of the skin and the growth of both the myoepithelial layer and the
smooth muscle Smooth muscle is an involuntary non-Striated muscle tissue, striated muscle, so-called because it has no sarcomeres and therefore no striated muscle tissue, striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit smoo ...
of the vagina. Typically estradiol will also cause pronounced growth of the
labia minora The labia minora (Latin for 'smaller lips', singular: ''labium minus'', 'smaller lip'), also known as the inner labia, inner lips, vaginal lips or nymphae are two flaps of skin on either side of the human vaginal opening in the vulva, situated be ...
and to a lesser degree of the
labia majora The labia majora (singular: ''labium majus'') are two prominent Anatomical terms of location, longitudinal Skin, cutaneous folds that extend downward and backward from the mons pubis to the perineum. Together with the labia minora they form the ...
. Estradiol is also responsible for the increased production of
pheomelanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
, resulting in the characteristic red color of the lips, labia minora and sometimes labia majora. Estradiol together with other ovarian steroids also cause the darker coloration of the
areola The human areola (''areola mammae'', or ) is the pigmented area on the breast around the nipple. Areola, more generally, is a small circular area on the Human body, body with a different histology from the surrounding Tissue (biology), tissu ...
. Testosterone will cause an enlargement of the
clitoris The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of #Other animals, other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), ...
and possibly has important effects on the growth and maturation of the
vestibular bulbs In female anatomy, the vestibular bulbs, bulbs of the vestibule or clitoral bulbs are two elongated masses of erectile tissue typically described as being situated on either side of the vaginal opening. They are united to each other in front by a ...
, corpus cavernosum of the clitoris and
urethral sponge The urethral sponge is a spongy cushion of tissue, found in the lower genital area of females, that sits against both the pubic bone and vagina In mammal Mammals () are a group of vertebrate animals constituting the class M ...
. Changes of the vulva initiated by estradiol as well as its direct effects also appear to influence the functioning of the lower urinary tract.


Underarm hair

Hair growth develops under the arms, starting out sparse before thickening and darkening over time.


Variations

In a general sense, the conclusion of puberty is reproductive maturity. Criteria for defining the conclusion may differ for different purposes: attainment of the ability to reproduce, achievement of maximal adult height, maximal gonadal size, or adult sex hormone levels. Maximal adult height is achieved at an average age of 15 years for an average girl and 18 years for an average boy. Potential fertility (sometimes termed ''nubility'') usually precedes completion of growth by 1–2 years in girls and 3–4 years in boys. Stage 5 typically represents maximal gonadal growth and adult hormone levels.


Age of onset

The definition of the onset of puberty may depend on perspective (e.g., hormonal versus physical) and purpose (establishing population normal standards, clinical care of early or late pubescent individuals, etc.). A common definition for the onset of puberty is physical changes to a person's body. These physical changes are the first visible signs of neural, hormonal, and gonadal function changes. The age at which puberty begins varies between individuals; usually, puberty begins between 10 and 13 years of age. The age at which puberty begins is affected by both genetic factors and by environmental factors such as nutritional state and social circumstances. An example of social circumstances is the Vandenbergh effect; a juvenile female who has significant interaction with adult males will enter puberty earlier than juvenile females who are not socially overexposed to adult males. The average age at which puberty begins may be affected by race as well. For example, the average age of
menarche Menarche ( ; ) is the first menstrual cycle, or first Menstruation, menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of f ...
in various populations surveyed has ranged from 12 to 18 years. The earliest average onset of puberty is for African-American girls and the latest average onset for high altitude subsistence populations in Asia. However, much of the higher age averages reflect nutritional limitations more than genetic differences and can change within a few generations with a substantial change in diet. The median age of menarche for a population may be an index of the proportion of undernourished girls in the population, and the width of the spread may reflect unevenness of wealth and food distribution in a population. Researchers have identified an earlier age of the onset of puberty. However, they have based their conclusions on a comparison of data from 1999 with data from 1969. In the earlier example, the sample population was based on a small sample of white girls (200, from Britain). The later study identified as puberty as occurring in 48% of African-American girls by age nine, and 12% of white girls by that age. Based on a publication from The Ribbon, a newsletter of the Cornell University Program on Breast Cancer and Environmental Risk Factors in New York States ((BCERF), Vol 6, No. 1, Winter 2001.) One possible cause of a delay in the onset of puberty past the age 14 in girls and 15 in boys is Kallmann syndrome, a form of
hypogonadotropic hypogonadism Hypogonadotropic hypogonadism (HH), is due to problems with either the hypothalamus or pituitary gland affecting the hypothalamic-pituitary-gonadal axis (HPG axis). Hypothalamic disorders result from a deficiency in the release of gonadotropic re ...
(HH). Kallmann syndrome is also associated with a lack of sense of smell (
anosmia Anosmia, also known as smell blindness, is the loss of the ability to detect one or more Odor, smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be due to ...
). Kallmann syndrome and other forms of HH affect both men and women. It is caused by a failure in HPG axis at puberty which results in low or zero
gonadotropin Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/chorionic ...
( LH and FSH) levels with the subsequent result of a failure to commence or complete puberty, secondary
hypogonadism Hypogonadism means diminished functional activity of the human gonad, gonads—the testicle, testes or the ovary, ovaries—that may result in diminished biosynthesis, production of sex hormones. Low androgen (e.g., testosterone) levels are refer ...
and
infertility Infertility is the inability of a person, animal or plant to Sexual reproduction, reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). I ...
.


Historical shift

The average age at which the onset of puberty occurs has dropped significantly since the 1840s. In every decade from 1840 to 1950 there was a drop of four months in the average age of menarche among Western European females. In
Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of ...
, girls born in 1840 had their menarche at an average age of 17 years. In France, the average in 1840 was 15.3 years. In
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separa ...
, the average in 1840 was 16.5 years. In
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, the decline happened later and was then more rapid: from 1945 to 1975 in Japan there was a drop of 11 months per decade. A 2006 study in Denmark found that puberty, as evidenced by breast development, started at an average age of 9 years and 10 months, a year earlier than when a similar study was done in 1991. Scientists believe the phenomenon could be linked to obesity or exposure to chemicals in the food chain, and is putting girls at greater long-term risk of breast cancer.


Genetic influence and environmental factors

Various studies have found direct genetic effects to account for at least 46% of the variation of timing of puberty in well-nourished populations. The genetic association of timing is strongest between mothers and daughters. The specific
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian inheritance#History, Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanin ...
s affecting timing are not yet known. Among the candidates is an
androgen receptor The androgen receptor (AR), also known as NR3C4 (nuclear receptor subfamily 3, group C, member 4), is a type of nuclear receptor that is activated by binding any of the androgenic hormones, including testosterone and dihydrotestosterone in the ...
gene. Researchers have hypothesized that early puberty onset may be caused by certain hair care products containing estrogen or placenta, and by certain chemicals, namely
phthalate Phthalates (, ), or phthalate esters, are ester In chemistry, an ester is a chemical compound, compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substi ...
s, which are used in many cosmetics, toys, and plastic food containers. If genetic factors account for half of the variation of pubertal timing, environment factors are clearly important as well. One of the first observed environmental effects is that puberty occurs later in children raised at higher altitudes. The most important of the environmental influences is clearly nutrition, but a number of others have been identified, all which affect timing of female puberty and menarche more clearly than male puberty.


Hormones and steroids

There is theoretical concern, and animal evidence, that environmental hormones and
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent Chemical element, elements by physical separation m ...
s may affect aspects of prenatal or postnatal sexual development in humans. Large amounts of incompletely metabolized estrogens and
progestogen Progestogens, also sometimes written progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptor, progesterone receptors (PR). Progesterone is the major and most important p ...
s from pharmaceutical products are excreted into the sewage systems of large cities, and are sometimes detectable in the environment.
Sex steroid Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are ...
s are sometimes used in cattle farming but have been banned in chicken meat production for 40 years. Although agricultural laws regulate use to minimize accidental human consumption, the rules are largely self-enforced in the United States. Significant exposure of a child to hormones or other substances that activate estrogen or androgen receptors could produce some or all of the changes of puberty. Harder to detect as an influence on puberty are the more diffusely distributed environmental chemicals like PCBs (
polychlorinated biphenyl Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act of 1976, Toxic Substances Contro ...
), which can bind and trigger estrogen receptors. More obvious degrees of partial puberty from direct exposure of young children to small but significant amounts of pharmaceutical sex steroids from exposure at home may be detected during medical evaluation for
precocious puberty In medicine, precocious puberty is puberty occurring at an unusually early age. In most cases, the process is normal in every aspect except the unusually early age and simply represents a human variability, variation of Human development (biology ...
, but mild effects and the other potential exposures outlined above would not.
Bisphenol A Bisphenol A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is Solubility, soluble in most common Solvent, organic solvents, but has very poor solubility in water. BPA is produc ...
(BPA) is a chemical used to make plastics, and is frequently used to make baby bottles, water bottles, sports equipment, medical devices, and as a coating in food and beverage cans. Scientists are concerned about BPA's behavioral effects on fetuses, infants, and children at current exposure levels because it can affect the prostate gland, mammary gland, and lead to early puberty in girls. BPA mimics and interferes with the action of estrogen—an important reproduction and development regulator. It leaches out of plastic into liquids and foods, and the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the National public health institutes, national public health agency of the United States. It is a Federal agencies of the United States, United States federal agency, under the United S ...
(CDC) found measurable amounts of BPA in the bodies of more than 90 percent of the U.S. population studied. The highest estimated daily intakes of BPA occur in infants and children. Many plastic baby bottles contain BPA, and BPA is more likely to leach out of plastic when its temperature is increased, as when one warms a baby bottle or warms up food in the microwave.


Nutritional influence

Nutrition Nutrition is the biochemistry, biochemical and physiology, physiological process by which an organism uses food to support its life. It provides organisms with Nutrient, nutrients, which can be Metabolism, metabolized to create energy and chem ...
al factors are the strongest and most obvious environmental factors affecting timing of puberty. Girls are especially sensitive to nutritional regulation because they must contribute all of the nutritional support to a growing fetus. Surplus
calorie The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of on ...
s (beyond growth and activity requirements) are reflected in the amount of
body fat Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the four primary types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the ...
, which signals to the brain the availability of resources for initiation of puberty and fertility. Much evidence suggests that for most of the last few centuries, nutritional differences accounted for majority of variation of pubertal timing in different populations, and even among social classes in the same population. Recent worldwide increased consumption of animal protein, other changes in nutrition, and increases in
childhood obesity Childhood obesity is a condition where excess adipose tissue, body fat negatively affects a child's health or well-being. As methods to determine body fat directly are difficult, the diagnosis of obesity is often based on Body mass index, BMI. ...
have resulted in falling ages of puberty, mainly in those populations with the higher previous ages. In many populations the amount of variation attributable to nutrition is shrinking. Although available dietary energy (simple calories) is the most important dietary influence on timing of puberty, quality of the diet plays a role as well. Lower
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metabo ...
intakes and higher
dietary fiber Dietary fiber (in British English fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition, and can be grouped generally by the ...
intakes, as occur with typical
vegetarian diet Vegetarian diet may refer to: *Vegetarianism Vegetarianism is the practice of abstaining from the Eating, consumption of meat (red meat, poultry, seafood, insects as food, insects, and the flesh of any other animal). It may also include abstaini ...
s, are associated with later onset and slower progression of female puberty.


Obesity influence and exercise

Scientific researchers have linked early
obesity Obesity is a medical condition, sometimes considered a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI) ...
with an earlier onset of puberty in girls. They have cited obesity as a cause of breast development before nine years and menarche before twelve years. Early puberty in girls can be a harbinger of later health problems. The average level of daily physical activity has also been shown to affect timing of puberty, especially in females. A high level of exercise, whether for athletic or body image purposes, or for daily subsistence, reduces energy calories available for reproduction and slows puberty. The exercise effect is often amplified by a lower body fat mass and cholesterol.


Physical and mental illness

Chronic diseases can delay puberty in both boys and girls. Those that involve chronic inflammation or interfere with nutrition have the strongest effect. In the western world,
inflammatory bowel disease Inflammatory bowel disease (IBD) is a group of inflammation, inflammatory conditions of the colon (anatomy), colon and small intestine, Crohn's disease and ulcerative colitis being the principal types. Crohn's disease affects the small intestine a ...
and
tuberculosis Tuberculosis (TB) is an infectious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
have been notorious for such an effect in the last century, while in areas of the underdeveloped world, chronic
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...
infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmiss ...
s are widespread. Mental illnesses occur in puberty. The brain undergoes significant development by
hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...
s which can contribute to mood disorders such as
major depressive disorder Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive depression (mood), low mood, low self-esteem, and anhedonia, loss of interest or pleasure in normally e ...
,
bipolar disorder Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of Depression (mood), depression and periods of abnormally elevated Mood (psychology), mood that last from days to weeks each. If the elevat ...
,
dysthymia Dysthymia ( ), also known as persistent depressive disorder (PDD), is a mental disorder, mental and Abnormal behaviour, behavioral disease#Disorder, disorder, specifically a disorder primarily of mood disorder, mood, consisting of similar cognit ...
and
schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social w ...
. Girls aged between 15 and 19 make up 40% of
anorexia nervosa Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by underweight, low weight, Calorie restriction, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thi ...
cases.


Stress and social factors

Some of the least understood environmental influences on timing of puberty are social and psychological. In comparison with the effects of genetics, nutrition, and general health, social influences are small, shifting timing by a few months rather than years. Mechanisms of these social effects are unknown, though a variety of physiological processes, including
pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s, have been suggested based on animal research. The most important part of a child's psychosocial environment is the family, and most of the social influence research has investigated features of family structure and function in relation to earlier or later female puberty. Most of the studies have reported that menarche may occur a few months earlier in girls in high-stress households, whose fathers are absent during their early childhood, who have a stepfather in the home, who are subjected to prolonged
sexual abuse Sexual abuse or sex abuse, also referred to as molestation, is abusive sexual behavior by one person upon another. It is often perpetrated using force or by taking advantage of another. Molestation often refers to an instance of sexual assau ...
in childhood, or who are
adopted Adoption is a process whereby a person assumes the parenting Parenting or child rearing promotes and supports the physical fitness, physical, emotional, Social change, social, spiritual and intellectual development of a child from infant, i ...
from a developing country at a young age. Conversely, menarche may be slightly later when a girl grows up in a large family with a biological father present. More extreme degrees of environmental stress, such as wartime refugee status with threat to physical survival, have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy. Most of these reported social effects are small and our understanding is incomplete. Most of these "effects" are statistical associations revealed by
epidemiologic Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and risk factor, determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decision ...
surveys. Statistical associations are not necessarily causal, and a variety of covariables and alternative explanations can be imagined. Effects of such small size can never be confirmed or refuted for any individual child. Furthermore, interpretations of the data are politically controversial because of the ease with which this type of research can be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism. Another limitation of the social research is that nearly all of it has concerned girls, partly because female puberty requires greater physiologic resources and partly because it involves a unique event (menarche) that makes survey research into female puberty much simpler than male. More detail is provided in the
menarche Menarche ( ; ) is the first menstrual cycle, or first Menstruation, menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of f ...
article.


Variations of sequence

The sequence of events of pubertal development can occasionally vary. For example, in about 15% of boys and girls, pubarche (the first pubic hairs) can precede, respectively, gonadarche and
thelarche Thelarche, also known as breast budding, is the onset of secondary breast development, often representing the beginning of pubertal development. It is the stage at which male and female breasts differentiate due to variance in hormone levels; howe ...
by a few months. Rarely,
menarche Menarche ( ; ) is the first menstrual cycle, or first Menstruation, menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of f ...
can occur before other signs of puberty in a few girls. These variations deserve medical evaluation because they can occasionally signal a disease.


Neurohormonal process

The endocrine
reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical sex organs, organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pherom ...
system consists of the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
, the
pituitary In vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, ...
, the
gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland that produces the Gamete, gametes and Sex hormone, sex hormones of an organism. Female reproductive cells are Egg cell, egg cells, and male reproductive cells are sp ...
s, and the
adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex whic ...
s, with input and regulation from many other body systems. True puberty is often termed "central puberty" because it begins as a process of the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
. A simple description of hormonal puberty is as follows: #The brain's
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
begins to release pulses of
GnRH Gonadotropin-releasing hormone (GnRH) is a releasing hormone Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are a ...
. #Cells in the
anterior pituitary A major organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard inst ...
respond by secreting LH and FSH into the circulation. #The ovaries or
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
respond to the rising amounts of LH and FSH by growing and beginning to produce
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous cycle, estrous and menstrual cycle, menstrual female reproductive cycles. Estradiol is resp ...
and
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate The prostate is both an Male accessory gland ...
. #Rising levels of estradiol and testosterone produce the body changes of female and male puberty. The onset of this neurohormonal process may precede the first visible body changes by 1–2 years.


Components of the endocrine reproductive system

The
arcuate nucleus The arcuate nucleus of the hypothalamus (also known as ARH, ARC, or infundibular nucleus) is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence. The arcuate nucleus includes several ...
of the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
is the driver of the reproductive system. It has
neuron A neuron, neurone, or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous ...
s which generate and release pulses of GnRH into the portal venous system of the
pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...
. The arcuate nucleus is affected and controlled by neuronal input from other areas of the brain and hormonal input from the
gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland that produces the Gamete, gametes and Sex hormone, sex hormones of an organism. Female reproductive cells are Egg cell, egg cells, and male reproductive cells are sp ...
s,
adipose Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the four primary types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the ...
tissue and a variety of other systems. The
pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...
responds to the pulsed GnRH signals by releasing LH and FSH into the blood of the general circulation, also in a pulsatile pattern. The gonads (
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
and ovaries) respond to rising levels of LH and FSH by producing the
steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...
sex hormones Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biolog ...
,
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate The prostate is both an Male accessory gland ...
and
estrogen Estrogen or oestrogen is a category of sex steroid, sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogeny (biology), endogenous estrogens th ...
. The
adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex whic ...
s are a second source for steroid hormones. Adrenal maturation, termed
adrenarche Adrenarche is an early stage in sexual maturation that happens in some higher primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and ...
, typically precedes gonadarche in mid-childhood.


Major hormones

* Neurokinin B (a tachykinin
peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptide ...
) and kisspeptin (a
neuropeptide Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...
), both present in KNDy neurons of the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
, are critical parts of the control system that switches on the release of GnRH at the start of puberty. *
GnRH Gonadotropin-releasing hormone (GnRH) is a releasing hormone Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are a ...
(
gonadotropin Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/chorionic ...
-releasing hormone) is a
peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptide ...
hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and beh ...
released from the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
which stimulates
gonadotrope Gonadotropic cells (called also Gonadotropes or Gonadotrophs or Delta Cells or Delta basophils) are endocrine cell (biology), cells in the anterior pituitary that produce the gonadotropins, such as the follicle-stimulating hormone (FSH) and luteini ...
cells of the anterior
pituitary In vertebrate Vertebrates () comprise all animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, ...
. * LH (luteinizing hormone) is a larger
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metabo ...
hormone secreted into the general circulation by gonadotrope cells of the anterior
pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The hypoph ...
. The main target cells of LH are the
Leydig cell Leydig cells, also known as interstitial cells of the testes and interstitial cells of Leydig, are found adjacent to the seminiferous tubules Seminiferous tubules are located within the testes, and are the specific location of meiosis, and the ...
s of
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
and the
theca cell The theca folliculi comprise a layer of the ovarian follicles. They appear as the follicles become secondary follicles. The theca are divided into two layers, the theca interna and the theca externa. Theca cells are a group of endocrine cells ...
s of the
ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
. LH secretion changes more dramatically with the initiation of puberty than FSH, as LH levels increase about 25-fold with the onset of puberty, compared with the 2.5-fold increase of FSH. * FSH ( follicle stimulating hormone) is another protein hormone secreted into the general circulation by the
gonadotrope Gonadotropic cells (called also Gonadotropes or Gonadotrophs or Delta Cells or Delta basophils) are endocrine cell (biology), cells in the anterior pituitary that produce the gonadotropins, such as the follicle-stimulating hormone (FSH) and luteini ...
cells of the anterior pituitary. The main target cells of FSH are the
ovarian follicle An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle. At the time of puberty, women have approximately 200,000 to 300,000 follicles, each with th ...
s and the
Sertoli cell Sertoli cells are a type of sustentacular "nurse" cell found in human testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the femal ...
s and
spermatogenic Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the Mitosis, mitotic division of the stem cells located close to the basement membrane of th ...
tissue of the
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
. *
Testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate The prostate is both an Male accessory gland ...
is a
steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...
hormone produced primarily by the
Leydig cell Leydig cells, also known as interstitial cells of the testes and interstitial cells of Leydig, are found adjacent to the seminiferous tubules Seminiferous tubules are located within the testes, and are the specific location of meiosis, and the ...
s of the
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is Homology (biology), homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, pr ...
, and in lesser amounts by the
theca cell The theca folliculi comprise a layer of the ovarian follicles. They appear as the follicles become secondary follicles. The theca are divided into two layers, the theca interna and the theca externa. Theca cells are a group of endocrine cells ...
s of the ovaries and the adrenal cortex. Testosterone is the primary mammalian
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This i ...
and the "original"
anabolic steroid Anabolic steroids, also known more properly as anabolic–androgenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone (medication), testosterone as well as synthetic androgens that are structurally related ...
. It acts on
androgen receptor The androgen receptor (AR), also known as NR3C4 (nuclear receptor subfamily 3, group C, member 4), is a type of nuclear receptor that is activated by binding any of the androgenic hormones, including testosterone and dihydrotestosterone in the ...
s in responsive tissue throughout the body. *
Estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous cycle, estrous and menstrual cycle, menstrual female reproductive cycles. Estradiol is resp ...
is a
steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...
hormone produced by
aromatization Aromatization is a chemical reaction in which an aromaticity, aromatic system is formed from a single nonaromatic precursor. Typically aromatization is achieved by dehydrogenation of existing cyclic compounds, illustrated by the conversion of cycl ...
of testosterone. Estradiol is the principal human
estrogen Estrogen or oestrogen is a category of sex steroid, sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogeny (biology), endogenous estrogens th ...
and acts on
estrogen receptor Estrogen receptors (ERs) are a group of proteins found inside cell (biology), cells. They are receptor (biochemistry), receptors that are activated by the hormone estrogen (17β-estradiol). Two classes of ER exist: nuclear estrogen receptors (ER ...
s throughout the body. The largest amounts of estradiol are produced by the
granulosa cell A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete (called an oocyte or egg) in the ovary of mammals. Structure and function In the Folliculogenesis#Primordial, primor ...
s of the
ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
, but lesser amounts are derived from
testicular A testicle or testis (plural testes) is the male Male (Mars symbol, symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilizati ...
and adrenal testosterone. * Adrenal
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This i ...
s are steroids produced by the zona reticulosa of the
adrenal cortex The adrenal cortex is the outer region and also the largest part of an adrenal gland. It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis. Each zone is responsible for producing specific hormones. It is ...
in both sexes. The major adrenal androgens are
dehydroepiandrosterone Dehydroepiandrosterone (DHEA), also known as androstenolone, is an endogenous steroid hormone precursor. It is one of the most abundant circulating steroids in humans. DHEA is produced in the adrenal glands, the gonads, and the brain. It functio ...
,
androstenedione Androstenedione, or 4-androstenedione (abbreviated as A4 or Δ4-dione), also known as androst-4-ene-3,17-dione, is an endogenous weak androgen steroid hormone and chemical intermediate, intermediate in the biosynthesis of estrone and of testost ...
(which are precursors of testosterone), and
dehydroepiandrosterone sulfate Dehydroepiandrosterone sulfate, abbreviated as DHEA sulfate or DHEA-S, also known as androstenolone sulfate, is an endogenous androstane steroid that is produced by the adrenal cortex. It is the 3β-sulfate ester and a metabolite of dehydroepiand ...
which is present in large amounts in the
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the Cell (biology), cells, and transports Metabolic waste, metabolic waste products away from th ...
. Adrenal androgens contribute to the androgenic events of early puberty in girls. * IGF1 (
insulin-like growth factor 1 Insulin-like growth factor 1 (IGF-1), also called somatomedin C, is a hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sen ...
) rises substantially during puberty in response to rising levels of
growth hormone Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone Peptide hormones or protein hormones are hormones whose molecules are peptide, or proteins, respectively. The latter h ...
and may be the principal mediator of the pubertal growth spurt. *
Leptin Leptin (from Ancient Greek, Greek λεπτός ''leptos'', "thin" or "light" or "small") is a hormone predominantly made by adipose cells and enterocytes in the small intestine that helps to regulate Energy homeostasis, energy balance by inhib ...
is a protein hormone produced by
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular en ...
. Its primary target organ is the
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalam ...
. The leptin level seems to provide the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
a rough indicator of adipose mass for purposes of regulation of
appetite Appetite is the desire to eat food items, usually due to Hunger (physiology), hunger. Appealing foods can stimulate appetite even when hunger is absent, although appetite can be greatly reduced by Hunger (motivational state), satiety. Appetite ex ...
and
energy metabolism Bioenergetics is a field in biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three ...
. It also plays a permissive role in female puberty, which usually will not proceed until an adequate body mass has been achieved.


Endocrine perspective

The endocrine reproductive system becomes functional by the end of the first trimester of fetal life. The testes and ovaries become briefly inactive around the time of birth but resume hormonal activity until several months after birth, when incompletely understood mechanisms in the brain begin to suppress the activity of the arcuate nucleus. This has been referred to as maturation of the prepubertal "gonadostat", which becomes sensitive to negative feedback by
sex steroid Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are ...
s. The period of hormonal activity until several months after birth, followed by suppression of activity, may correspond to the period of infant sexuality, followed by a
latency stage The latency stage is the fourth stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', ...
, which
Sigmund Freud Sigmund Freud ( , ; born Sigismund Schlomo Freud; 6 May 1856 – 23 September 1939) was an Austrian neurologist and the founder of psychoanalysis, a clinical method for evaluating and treating psychopathology, pathologies explained as originatin ...
described.
Gonadotropin Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. This family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/chorionic ...
and sex steroid levels fall to low levels (nearly undetectable by current clinical assays) for approximately another 8 to 10 years of childhood. Evidence is accumulating that the reproductive system is not totally inactive during the childhood years. Subtle increases in gonadotropin pulses occur, and ovarian follicles surrounding
germ cell Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during emb ...
s (future
egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo An embryo is an initial stage of development of a multicellular organism. In organisms that Sexual repr ...
s) double in number. Normal puberty is initiated in the hypothalamus, with de-inhibition of the pulse generator in the arcuate nucleus. This inhibition of the arcuate nucleus is an ongoing active suppression by other areas of the brain. The signal and mechanism releasing the arcuate nucleus from inhibition have been the subject of investigation for decades and remain incompletely understood.
Leptin Leptin (from Ancient Greek, Greek λεπτός ''leptos'', "thin" or "light" or "small") is a hormone predominantly made by adipose cells and enterocytes in the small intestine that helps to regulate Energy homeostasis, energy balance by inhib ...
levels rise throughout childhood and play a part in allowing the arcuate nucleus to resume operation. If the childhood inhibition of the arcuate nucleus is interrupted prematurely by injury to the brain, it may resume pulsatile gonadotropin release and puberty will begin at an early age. Neurons of the arcuate nucleus secrete
gonadotropin releasing hormone Gonadotropin-releasing hormone (GnRH) is a releasing hormone Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release. They are a ...
(GnRH) into the blood of the pituitary portal system. An American physiologist, Ernst Knobil, found that the GnRH signals from the hypothalamus induce pulsed secretion of LH (and to a lesser degree, FSH) at roughly 1–2 hour intervals. The LH pulses are the consequence of pulsatile GnRH secretion by the arcuate nucleus that, in turn, is the result of an
oscillator Oscillation is the repetitive or Periodic function, periodic variation, typically in time, of some measure about a central value (often a point of Mechanical equilibrium, equilibrium) or between two or more different states. Familiar examples o ...
or signal generator in the central nervous system ("GnRH pulse generator"). In the years preceding physical puberty, Robert M. Boyar discovered that the gonadotropin pulses occur only during sleep, but as puberty progresses they can be detected during the day. By the end of puberty, there is little day-night difference in the amplitude and frequency of gonadotropin pulses. Some investigators have attributed the onset of puberty to a
resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied Periodic function, periodic force (or a Fourier analysis, Fourier component of it) is equal or close to a natural frequency of the system ...
of oscillators in the brain. By this mechanism, the gonadotropin pulses that occur primarily at night just before puberty represent beats. An array of "autoamplification processes" increases the production of all of the pubertal hormones of the hypothalamus, pituitary, and gonads. Regulation of
adrenarche Adrenarche is an early stage in sexual maturation that happens in some higher primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and ...
and its relationship to maturation of the hypothalamic-gonadal axis is not fully understood, and some evidence suggests it is a parallel but largely independent process coincident with or even preceding central puberty. Rising levels of adrenal
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This i ...
s (termed adrenarche) can usually be detected between 6 and 11 years of age, even before the increasing gonadotropin pulses of hypothalamic puberty. Adrenal androgens contribute to the development of pubic hair ( pubarche), adult
body odor Body odor or body odour (BO) is present in all animals and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis, but can also be strongly influenced by various diseases ...
, and other androgenic changes in both sexes. The primary clinical significance of the distinction between adrenarche and gonadarche is that pubic hair and body odor changes by themselves do not prove that central puberty is underway for an individual child.


Hormonal changes in boys

Early stages of male hypothalamic maturation seem to be very similar to the early stages of female puberty, though occurring about 1–2 years later. LH stimulates the Leydig cells of the testes to make testosterone and blood levels begin to rise. For much of puberty, nighttime levels of testosterone are higher than daytime. Regularity of frequency and amplitude of gonadotropin pulses seems to be less necessary for progression of male than female puberty. However, a significant portion of
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate The prostate is both an Male accessory gland ...
in adolescent boys is converted to estradiol. Estradiol mediates the growth spurt, bone maturation, and epiphyseal closure in boys just as in girls. Estradiol also induces at least modest development of breast tissue (
gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of Breast#Anatomy, breast tissue as a result of a endocrine disorder, hormone imbalance between estrogens and ...
) in a large proportion of boys. Boys who develop mild gynecomastia, a swellings under
nipple The nipple is a raised region of tissue on the surface of the breast from which, in females, breast milk, milk leaves the breast through the lactiferous ducts to feed an infant. The milk can flow through the nipple passively or it can be ejected ...
s, during puberty are told the effects are temporary in some male teenagers due to high levels of
estradiol Estradiol (E2), also spelled oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of the estrous cycle, estrous and menstrual cycle, menstrual female reproductive cycles. Estradiol is resp ...
. Another hormonal change in males takes place during the teenage years for most young men. At this point in a male's life the testosterone levels slowly rise, and most of the effects are mediated through the androgen receptors by way of conversion
dihydrotestosterone Dihydrotestosterone (DHT, 5α-dihydrotestosterone, 5α-DHT, androstanolone or stanolone) is an endogenous androgen sex steroid and hormone. The enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical ...
in target organs (especially that of the bowels).


Hormonal changes in girls

As the amplitude of LH pulses increases, the theca cells of the ovaries begin to produce testosterone and smaller amounts of
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major ...
. Much of the testosterone moves into nearby cells called
granulosa cell A granulosa cell or follicular cell is a somatic cell of the sex cord that is closely associated with the developing female gamete (called an oocyte or egg) in the ovary of mammals. Structure and function In the Folliculogenesis#Primordial, primor ...
s. Smaller increases of FSH induce an increase in the
aromatase Aromatase (), also called estrogen synthetase or estrogen synthase, is an enzyme responsible for a key step in the biosynthesis of estrogens. It is CYP19A1, a member of the cytochrome P450 superfamily, which are monooxygenases that catalyze many ...
activity of these granulosa cells, which converts most of the testosterone to estradiol for secretion into the circulation. The remaining testosterone, together with adrenal androgens is responsible for the typical androgenic changes of female puberty: pubic hair, other androgenic hair as outlined above, body odor, acne. The bioactivity of testosterone is to a large degree limited by SHBG which in turn is mainly controlled by estradiol and
prolactin Prolactin (PRL), also known as lactotropin, is a protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions w ...
levels (estradiol stimulates, prolactin decreases SHBG synthesis). Rising levels of estradiol produce the characteristic estrogenic body changes of female puberty: growth spurt, acceleration of bone maturation and closure,
breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryology, embryological tissues. In females, it serves as the mammary gland, which produce ...
growth, increased fat composition, growth of the uterus, increased thickness of the
endometrium The endometrium is the inner epithelium, epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The funct ...
and the vaginal mucosa, and widening of the lower pelvis. As the estradiol levels gradually rise and the other autoamplification processes occur, a point of maturation is reached when the feedback sensitivity of the hypothalamic "gonadostat" becomes positive. This attainment of positive feedback is the hallmark of female sexual maturity, as it allows the mid cycle LH surge necessary for
ovulation Ovulation is the release of egg cells, eggs from the ovaries. In women, this event occurs when the ovarian follicles rupture and release the secondary oocyte ovarian cells. After ovulation, during the luteal phase, the egg will be available to be ...
. Growth hormone levels rise steadily throughout puberty. IGF1 levels rise and then decline as puberty ends. Growth finishes and adult height is attained as the estradiol levels complete closure of the
epiphyses The epiphysis () is the rounded end of a long bone, at its joint with adjacent bone(s). Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, including the epiphyseal plate (growth plate). At the join ...
.


Stages

*
adrenarche Adrenarche is an early stage in sexual maturation that happens in some higher primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and ...
(approximately age 11) * gonadarche (approximately age 8) *
thelarche Thelarche, also known as breast budding, is the onset of secondary breast development, often representing the beginning of pubertal development. It is the stage at which male and female breasts differentiate due to variance in hormone levels; howe ...
(approximately age 11 in females) * pubarche (approximately age 12) *
menarche Menarche ( ; ) is the first menstrual cycle, or first Menstruation, menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of f ...
(approximately age 12.5 in females) *
spermarche Spermarche—also known as semenarche—is the beginning of development of sperm in boys' testicles at puberty.''Adolescence and Emerging Adulthood: A Cultural Approach'', Jeffrey Jensen Arnett, N.J.: Prentice-Hall, 3rd edition, 2006. It is the c ...
(approximately age 13.5 in males)


See also

*
Adolescent sexuality Adolescent sexuality is a stage of human development Human development may refer to: * Development of the human body * Developmental psychology * Human development (economics) * Human Development Index, an index used to rank countries by level o ...
*
Child sexuality Development of Human sexuality, sexuality is an integral part of the development and maturation of children. It includes a range of sensory, emotional, and consequent sexual activity, sexual activities that may occur before or during early puberty, ...
*
Delayed puberty Delayed puberty is when a person lacks or has incomplete development of specific sexual characteristics past the usual age of onset of puberty. The person may have no physical or hormone, hormonal signs that puberty has begun. In the United States, ...
*
Eunuch A eunuch ( ) is a male who has been castration, castrated. Throughout history, castration often served a specific social function. The earliest records for intentional castration to produce eunuchs are from the Sumerian city of Lagash in the 2n ...
*
Hebephilia Hebephilia is the strong, persistent sexual interest by adults in pubescent children who are in early adolescence, typically ages 11–14 and showing Tanner stages 2 to 3 of physical development. It differs from pedophilia (the primary or excl ...
* Kallmann syndrome *
Precocious puberty In medicine, precocious puberty is puberty occurring at an unusually early age. In most cases, the process is normal in every aspect except the unusually early age and simply represents a human variability, variation of Human development (biology ...
* Puberphonia *
Secondary sex characteristic Secondary sex characteristics are features that appear during puberty in human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedality, bipedalism and exceptional cognitive skills due ...
* Puberty blocker * Seclusion of girls at puberty


References


Sources

* * * * *


Further reading

* Colburn, T., Dumanoski, D. and Myers, J.P. Our Stolen Future, 1996, Plume: New York. * Ducros, A. and Pasquet, P. "Evolution de l'âge d'apparition des premières règles (ménarche) en France". ''Biométrie Humaine'' (1978), 13, 35–43. * * Newer data suggesting that lower age thresholds for evaluation should be used. * Plant TM, Lee PA, eds. ''The Neurobiology of Puberty''. Bristol: Society for Endocrinology, 1995. Proceedings of the latest (4th) International Conference on the Control of the Onset of Puberty, containing summaries of current theories of physiological control, as well as GnRH analog treatment. *Sizonenko, PC
Role of sex steroids during development—integration
in Bourguignon, Jean Pierre & Tony M. Plant. The Onset of Puberty in Perspective: Proceedings of the 5th International Conference on the Control of the Onset of Puberty, Held in Liège, Belgium, 26–28 September 1999. Elsevier. Amsterdam & New York 2000. . pp 299–306. * Highly useful growth charts with integrated standards for stages of puberty. *

''ScienceDaily'', December 1, 2005


External links


Support for teens
(archive)
University of Maryland guide to puberty and adolescenceGrowing Up Sexually: A World AtlasPictures and detailed information about breast development during puberty

Puberty in girls: interactive animation of Tanner stages

Puberty in boys: interactive animation of Tanner stages
{{Authority control Adolescence Human development Human female endocrine system Sexuality and age