Lanugo is very thin, soft, usually unpigmented, downy
hair that is sometimes found on the body of a fetus or
newborn
An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...
. It is the first hair to be produced by the fetal hair follicles, and it usually appears around sixteen weeks of gestation and is abundant by week twenty. It is normally shed before birth, around seven or eight months of gestation, but is sometimes present at birth. It disappears on its own within a few weeks.
It is replaced by hair covering the same surfaces, which is called
vellus hair
Vellus hair is short, thin, light-colored, and barely noticeable hair that develops on most of a human’s body during childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital ...
. This hair is thinner and more difficult to see. The more visible hair that persists into
adulthood is called
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.Marks, James G; Miller, Jeffery (2006)''Lookingbill and M ...
. It forms in specific areas and is
hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
-dependent. The term is from the
Latin
Latin (, or , ) is a classical language belonging to the 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 the power of the ...
''
lana
Lana may refer to:
*Lana (given name)
*Francesco Lana de Terzi (1631–1687), Italian Jesuit priest and scientist
*Lana (wrestler), professional wrestler and pro wrestling manager
*''Wild Energy. Lana'', a 2006 Ukrainian fantasy novel
Sciences
*L ...
'', meaning "wool."
Humans
Fetal development
During human development, the lanugo grows on
fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
es as a normal part of
gestation, but it is usually shed and replaced by
vellus hair
Vellus hair is short, thin, light-colored, and barely noticeable hair that develops on most of a human’s body during childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital ...
at about thirty-three to thirty-six weeks of
gestational age
In obstetrics, gestational age is a measure of the age of a pregnancy which is taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method if available. Su ...
. As the lanugo is shed from the skin, it is normal for the hair to be consumed by the developing fetus, since it drinks from the
amniotic fluid and urinates into its environment. As a result, lanugo contributes to the new-born baby's
meconium. The presence of lanugo on new-borns is not necessarily a sign of
premature birth
Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between 2 ...
, as it is also seen on infants born at thirty-nine weeks of gestation (full term).
Lanugo functions as an anchor to hold the
vernix caseosa
Vernix caseosa, also known as vernix or birthing custard, is the waxy white substance found coating the skin of newborn human babies. It is produced by dedicated cells and is thought to have some protective roles during fetal development and for ...
on the skin. Together they protect the delicate fetal skin from being damaged by the amniotic fluid. The vernix caseosa also helps to prepare the fetus for life outside the womb. It provides lubrication for birth and contributes to thermoregulation, prevention of water loss, and innate immunity. Without the lanugo to anchor the vernix caseosa, these functions would be compromised.
Malnutrition
In the absence of
fat
In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.
The term often refers specifically to triglycerides (triple est ...
, lanugo grows to serve as a replacement
insulator, and thus can be observed in malnourished patients, including those with eating disorders. When found along with other physical symptoms, for example, lanugo can help a physician make a diagnosis of
anorexia nervosa
Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gr ...
or
bulimia nervosa
Bulimia nervosa, also known as simply bulimia, is an eating disorder characterized by binge eating followed by purging or fasting, and excessive concern with body shape and weight. The aim of this activity is to expel the body of calories eaten ...
.
Teratoma
It is often found in
teratoma
A teratoma is a tumor made up of several different types of tissue, such as hair, muscle, teeth, or bone. Teratomata typically form in the ovary, testicle, or coccyx.
Symptoms
Symptoms may be minimal if the tumor is small. A testicular ter ...
s (congenital tumours).
Other mammals
Lanugo is also common on other
mammals
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur o ...
. For example, seals
and elephants are often born with a covering of lanugo. Some species of fetal whales and dolphins also have lanugo.
References
External links
{{Authority control
Human hair
Neonatology