The nipple is a raised region of tissue on the surface of the

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 embryological tissues. In females, it serves as the mammary gland, which produces and sec ...

from which, in females,

milk Milk is a white liquid food produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals (including breastfed human infants) before they are able to digest solid food. Immune factors and immune-modula ...

leaves the breast through the

lactiferous duct Lactiferous ducts are ducts that converge and form a branched system connecting the nipple to the lobules of the mammary gland. When lactogenesis occurs, under the influence of hormones, the milk is moved to the nipple by the action of smooth mus ...

s to feed an infant. The milk can flow through the nipple passively or it can be ejected by

smooth Smooth may refer to: Mathematics * Smooth function, a function that is infinitely differentiable; used in calculus and topology * Smooth manifold, a differentiable manifold for which all the transition maps are smooth functions * Smooth algebrai ...

muscle contractions that occur along with the ductal system. The nipple is surrounded by 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 ...

, which is often a darker colour than the surrounding skin. A nipple is often called a

teat A teat is the projection from the mammary glands of mammals from which milk flows or is ejected for the purpose of feeding young. In many mammals the teat projects from the udder. The number of teats varies by mammalian species and often corr ...

when referring to non-humans. Nipple or teat can also be used to describe the flexible mouthpiece of a

baby bottle A baby bottle, nursing bottle, or feeding bottle is a bottle with an attached ''teat'' (also called a ''nipple'' in the US) on the top opening, on which can be suckled, and from thereby drunk directly. It is typically used by infants and young ...

. In humans, the nipples of both males and females can be stimulated as part of sexual arousal. In many cultures, human female nipples are sexualized, or "regarded as sex objects and evaluated in terms of their physical characteristics and sexiness."

Anatomy

In mammals, a nipple (also called mammary papilla or

) is a small projection of

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 animal coverings, such as the arthropod exoskeleton, have different de ...

containing the outlets for 15–20

s arranged cylindrically around the tip.

Marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s and eutherian mammals typically have an even number of nipples arranged bilaterally, from as few as 2 to as many as 19. The skin of the nipple is rich in a supply of special nerves that are sensitive to certain stimuli: these are slowly-adapting and rapidly-adapting

cutaneous 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 animal coverings, such as the arthropod exoskeleton, have different d ...

mechanoreceptors. Mechanoreceptors are identified respectively by Type I slowly-adapting with multiple

Merkel corpuscle end-organ Merkel nerve endings are mechanoreceptors, a type of sensory receptor, that are found in the basal epidermis and hair follicles. They are nerve endings and provide information on mechanical pressure, position, and deep static touch features, su ...

s and Type II slowly-adapting with single Ruffini corpuscle end-organs, as well as Type I rapidly-adapting with multiple

Meissner corpuscle end-organ Tactile corpuscles or Meissner's corpuscles are a type of mechanoreceptor discovered by anatomist Georg Meissner (1829–1905) and Rudolf Wagner. This corpuscle is a type of nerve ending in the skin that is responsible for sensitivity to pressur ...

s and Type II rapidly-adapting with single

Pacinian corpuscle end-organs Pacinian corpuscle or lamellar corpuscle or Vater-Pacini corpuscle; is one of the four major types of mechanoreceptors (specialized nerve ending with adventitious tissue for mechanical sensation) found in mammalian skin. This type of mechanorece ...

. The dominant nerve supply to the nipple comes from the lateral cutaneous branches of fourth

intercostal nerve The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and diff ...

. The nipple is also used as an anatomical landmark. It marks the T4 (fourth thoracic vertebra) dermatome and rests over the approximate level of the diaphragm. The arterial supply to the nipple and breast originates from the anterior intercostal branches of the internal thoracic (mammary) arteries; lateral thoracic artery; and thoracodorsal arteries. The venous vessels parallel the arteries. The lymphatic ducts that drain the nipple are the same for the breast. The axillary nodes are the apical axillary nodes, the lateral group and the anterior group. 75% of the lymph is drained through the axillary lymph nodes located near the armpit. The rest of the drainage leaves the nipple and breast through infroclavicular, pectoral, or parasternal nodes. Since nipples change throughout the life span in men and women, the anatomy of the nipple can change and this change may be expected and considered normal.

In male mammals

Almost all

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 ...

have nipples. Why males have nipples has been the subject of scientific research. Differences among the sexes (called

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

) within a given species are considered by

evolutionary biologist Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life for ...

s to be mostly the result of

sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ( ...

, directly or indirectly. There is a consensus that the male nipple exists because there is no particular advantage to males losing the trait (this is called a

spandrel A spandrel is a roughly triangular space, usually found in pairs, between the top of an arch and a rectangular frame; between the tops of two adjacent arches or one of the four spaces between a circle within a square. They are frequently fill ...

Function

The physiological purpose of nipples is to deliver

, produced in the female

mammary gland A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in pri ...

s during

lactation Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process naturally occurs with all sexually mature female mammals, although it may predate mammals. The proces ...

, to an infant. During breastfeeding, nipple stimulation by an infant will stimulate the release of oxytocin 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 hypothalamu ...

. Oxytocin is a

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 ...

that increases during pregnancy and acts on the breast to help produce the milk-ejection reflex. Oxytocin release from the nipple stimulation of the infant causes the uterus to contract even after childbirth. The strong uterine contractions that are caused by the stimulation of the mother's nipples help the uterus contract to clamp down the uterine arteries. These contractions are necessary to prevent post-partum haemorrhage. When the infant suckles or stimulates the nipple, oxytocin levels rise and small muscles in the breast contract, moving the milk through the milk ducts. The result of nipple stimulation by the infant helps to move breast milk out through the ducts and to the nipple. This contraction of milk is called the "let-down reflex". Latching on refers to the infant fastening onto the nipple to breastfeed. A good attachment is when the bottom of the areola (the area around the nipple) is in the infant's mouth and the nipple is drawn back inside his or her mouth. A poor latch results in insufficient nipple stimulation to create the let down reflex. The nipple is poorly stimulated when the baby latches on too close to the tip of the nipple. This poor attachment can cause sore and

cracked nipple Cracked nipple (nipple trauma or nipple fissure) is a condition that can occur in breastfeeding women as a result of a number of possible causes. Developing a cracked nipple can result in soreness, dryness or irritation to, or bleeding of, one or ...

s and a reluctance of the mother to continue to breastfeed. After birth, the milk supply increases based upon the continuous and increasing stimulation of the nipple by the infant. If the baby increases nursing time at the nipple, the mammary glands respond to this stimulation by increasing milk production.

Clinical significance

Pain

Nipple pain can be a disincentive for breastfeeding. Sore nipples that progress to cracked nipples is of concern since many women cease breastfeeding due to the pain. In some instances, an ulcer will form on the nipple. One reason for the development of cracked and sore nipples is the incorrect latching-on of the infant to the nipple. If a nipple appears to be wedge-shaped, white and flattened, this may indicate that the attachment of the infant is not good and there is a potential of developing cracked nipples. Herpes infection of the nipple is painful. Nipple pain can also be caused by excessive

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

of clothing against the nipple that causes a

fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure ...

Discharge

Nipple discharge refers to any fluid that seeps out of the nipple of the breast. Discharge from the nipple does not occur in lactating women. And discharge in non-pregnant women or women who are not breastfeeding may not cause concern. Men that have discharge from their nipples are not typical. Discharge from the nipples of men or boys may indicate a problem. Discharge from the nipples can appear without squeezing or may only be noticeable if the nipples are squeezed. One nipple can have discharge while the other does not. The discharge can be clear, green, bloody, brown or straw-coloured. The consistency can be thick, thin, sticky or watery. Some cases of nipple discharge will clear on their own without treatment. Nipple discharge is most often not cancer (benign), but rarely, it can be a sign of breast cancer. It is important to determine what is causing the discharge and to get treatment. Reasons for nipple discharge include: * Pregnancy * Recent breastfeeding *

Rubbing A rubbing ('' frottage'') is a reproduction of the texture of a surface created by placing a piece of paper or similar material over the subject and then rubbing the paper with something to deposit marks, most commonly charcoal or pencil but ...

on the area from a bra or T-shirt * Injury to the breast *

Infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...

* Inflammation and clogging of the breast ducts * Noncancerous

pituitary tumor Pituitary adenomas are tumors that occur in the pituitary gland. Most pituitary tumors are benign, approximately 35% are invasive and just 0.1% to 0.2% are carcinomas.growth in the breast (usually not cancer) * Severe underactive thyroid gland ( hypothyroidism) * Fibrocystic breast (normal lumpiness in the breast) * Use of certain medicines * Use of certain herbs, such as anise and fennel * Widening of the milk ducts Sometimes, babies can have nipple discharge. This is caused by hormones from the mother before birth. It usually goes away in two weeks. Cancers such as Paget's disease (a rare type of cancer involving the skin of the nipple) can also cause nipple discharge. Nipple discharge that is not normal is bloody, comes from only one nipple, or comes out on its own without squeezing or touching the nipple. Nipple discharge is more likely to be normal if it comes out of both nipples or happens when the nipples are squeezed. Squeezing the nipple to check for discharge can make it worse. Leaving the nipple alone may make the discharge stop. Nipple discharge in a male is usually of more concern. Most of the time a mammogram and an examination of the fluid is done. A biopsy is often performed. A fine needle aspiration (FNA) biopsy can be fast and least painful. A very thin, hollow needle and slight suction will be used to remove a small sample from under the nipple. Using a local anesthetic to numb the skin may not be necessary since a thin needle is used for the biopsy. Receiving an injection to prevent pain from the biopsy may be more painful than the biopsy itself. Some men develop a condition known as

gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Updated by Brent Wisse ( ...

, in which the breast tissue under the nipple develops and grows. Discharge from the nipple can occur. The nipple may swell in some men possibly due to increased levels of estrogen.

Appearance

Changes in appearance may be normal or related to disease. *

Inverted nipple An inverted nipple (occasionally invaginated nipple) is a condition where the nipple, instead of pointing outward, is retracted into the breast. In some cases, the nipple will be temporarily protruded if stimulated. Both women and men can have inv ...

s – This is normal if the nipples have always been indented inward and can easily point out when touched. If the nipples are pointing in and this is new, this is an unexpected change. * Skin puckering of the nipple – This can be caused by scar tissue from surgery or an infection. Often, scar tissue forms for no reason. Most of the time this issue does not need treatment. This is an unexpected change. This change can be of concern since puckering or retraction of the nipple can indicate an underlying change in breast tissue that may be cancerous. * The nipple is warm to the touch, red or painful – This can be an infection. It is rarely due to breast cancer. * Scaly, flaking, or itchy nipple – This is most often due to

eczema Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...

or a bacterial or fungal infection. This change is not expected. Flaking, scaly, or itchy nipples can be a sign of Paget's disease. * Thickened skin with large pores – This is called peau d'orange because the skin looks like an orange peel. An infection in the breast or inflammatory breast cancer can cause this problem. This is not an expected change. * Retracted nipples – The nipple was raised above the surface but changes, begins to pull inward, and does not come out when stimulated. The average projection and size of human female nipples is slightly more than .

Breast cancer

Symptoms of

breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a r ...

can often be seen first by changes of the nipple and areola, although not all women have the same symptoms, and some people do not have any signs or symptoms at all. A person may find out they have breast cancer after a routine

mammogram Mammography (also called mastography) is the process of using low-energy X-rays (usually around 30 Peak kilovoltage, kVp) to examine the human breast for diagnosis and screening. The goal of mammography is the early detection of breast cancer, ty ...

. Warning signs can include: * New lump in the nipple, or breast or armpit * Thickening or swelling of part of the breast, areola, or nipple * Irritation or dimpling of breast skin * Redness or flaky skin in the nipple area or the breast * Pulling in of the nipple or pain in the nipple area * Nipple discharge other than breast milk, including blood * Any change in the size or the shape of the breast or nipple * Pain in any area of the breast Changes in the nipple are not necessarily symptoms or signs of breast cancer. Other conditions of the nipple can mimic the signs and symptoms of breast cancer.

Vertical transmission

Some infections are transmitted through the nipple, especially if irritation or injury to the nipple has occurred. In these circumstances, the nipple itself can become infected with Candida that is present in the mouth of the breastfeeding infant. The infant will transmit the infection to the mother. Most of the time, this infection is localized to the area of the nipple. In some cases, the infection can progress to become a full-blown case of

mastitis Mastitis is inflammation of the breast or udder, usually associated with breastfeeding. Symptoms typically include local pain and redness. There is often an associated fever and general soreness. Onset is typically fairly rapid and usually occurs ...

or breast infection. In some cases, if the mother has an infection with no nipple cracks or ulcerations, it is still safe to breastfeed the infant.

Herpes infection Herpes simplex is a viral infection caused by the herpes simplex virus. Infections are categorized based on the part of the body infected. Oral herpes involves the face or mouth. It may result in small blisters in groups often called cold s ...

of the nipple can go unnoticed because the lesions are small but usually are quite painful. Herpes in the newborn is a serious and sometimes fatal infection. Transmission of Hepatitis C and B to the infant can occur if the nipples are cracked. Other infections can be transmitted through a break of the skin of the nipple and can infect the infant.

Other disorders

Nipple bleb A nipple bleb is a blister on the nipple that can be filled with serous or other fluid. It may be pink or light yellow. It is thin-walled and may appear as a small blister, more than 5 mm in diameter. It can also be referred to as a bulla. So ...

* Candida infection of the nipple *Eczema of the nipple *

* Staphylococcus infection of the nipple * Edematous areola *

of the nipple * Reynaud phenomenon of the nipple * Flat nipple

Surgery

A nipple-sparing/ subcutaneous mastectomy is a surgical procedure where breast tissue is removed, but the nipple and areola are preserved. This procedure was historically done only prophylactically or with mastectomy for the benign disease over the fear of increased cancer development in retained areolar ductal tissue. Recent series suggest that it may be an oncologically sound procedure for tumours not in the subareolar position.

Society and culture

Duplessis's semi-topless portrait of the Princess of Lamballe dates from 18th Century France

Exposure

The culture tendency to hide the female nipple under clothing has existed in Western culture since the 1800s. As female nipples are often perceived an

intimate part An intimate part, personal part or private part is a place on the human body which is customarily kept covered by clothing in public venues and conventional settings, as a matter of fashion and cultural norms. In several cultures, revealing these p ...

, covering them might have originated under

Victorian morality Victorian morality is a distillation of the moral views of the middle class in 19th-century Britain, the Victorian era. Victorian values emerged in all classes and reached all facets of Victorian living. The values of the period—which can be ...

as with riding side saddle. Exposing the entire breast and nipple is a form of protest for some and a crime for others. The exposure of nipples is usually considered immodest and in some instances is viewed as lewd or indecent behavior. A case in Erie, Pennsylvania, concerning the exposure of breasts and nipple proceeded to the US Supreme Court. The Erie ordinance was regulating the nipple in public as an act that is committed when a person "knowingly or intentionally, ... appears in a state of nudity commits Public Indecency." Later in the statute, nudity is further described as an uncovered female nipple. But nipple exposure of a man was not regulated. An opinion column credited to

Cecil Adams Cecil Adams is the pseudonymous author of ''The Straight Dope'', a popular question and answer column published in ''The Chicago Reader'' from 2 February 1973 to 2018. The true identity of Adams, whether a single individual or a group of authors ...

noted: "Ponder the significance of that. A man walks around bare-chested and the worst that happens is he won't get served in restaurants. But a woman who goes topless is legally in the same boat as if she'd had sex in public. That may seem crazy, but in the US it's a permissible law." Namibie Himba 0716a

The legality around the exposure of nipples is inconsistently regulated throughout the US. Some states do not allow the visualization of any part of the breast. Other jurisdictions prohibit any female chest anatomy by banning anatomical structures that lie below the top of the areola or nipple. Such is the case in West Virginia and Massachusetts. West Virginia's regulation is very specific and is not likely to be misinterpreted, stating: " hedisplay of 'any portion of the cleavage of the human female breast exhibited by a dress, blouse, skirt, leotard, bathing suit, or other wearing apparel s permittedprovided the areola is not exposed, in whole or in part. Instagram has a "no nipples" policy with exceptions: material that is not allowed includes "some photos of female nipples, but photos of post-mastectomy scarring and women actively breastfeeding are allowed. Nudity in photos of paintings and sculptures is OK, too". Previously, Instagram had removed images of nursing mothers. Instagram removed images of Rihanna and had her account cancelled in 2014 when she posted selfies with nipples. This was incentive for the Twitter campaign #FreeTheNipple. In 2016, an Instagram page invited users to post images of nipples from both sexes; @genderless_nipples, which displays close ups of both the nipples of men and women for the purpose of spotlighting what may be inconsistency. Some contributors have circumvented the policy. Facebook has also been struggling to define its nipple policy. Filmmaker Lina Esco made a film entitled ''

Free the Nipple Free the Nipple is a topfreedom campaign created in 2012 during pre-production of a 2014 film of the same name. The campaign highlights the general convention of allowing men to appear topless in public while considering it sexual or indecent f ...

'', which is about "laws against female toplessness or restrictions on images of female, but not male, nipples", which Esco states is an example of

sexism Sexism is prejudice or discrimination based on one's sex or gender. Sexism can affect anyone, but it primarily affects women and girls.There is a clear and broad consensus among academic scholars in multiple fields that sexism refers pri ...

in society.

Sexuality

Nipples can be sensitive to touch, and

nipple stimulation Nipple stimulation or breast stimulation is stimulation of the breast. Stimulation may be by breastfeeding, sexual activity, or an indirect non-sexual response. As part of sexual activity, the practice may be performed upon, or by, people of any ...

can incite sexual arousal. Few women report experiencing

orgasm Orgasm (from Greek , ; "excitement, swelling") or sexual climax is the sudden discharge of accumulated sexual excitement during the sexual response cycle, resulting in rhythmic, involuntary muscular contractions in the pelvic region chara ...

from nipple stimulation. Before Komisaruk et al.'s functional magnetic resonance (fMRI) research on nipple stimulation in 2011, reports of women achieving orgasm from nipple stimulation relied solely on anecdotal evidence. Komisaruk's study was the first to map the female genitals onto the sensory portion of the brain; it indicates that sensation from the nipples travels to the same part of the brain as sensations from the vagina, clitoris and cervix, and that these reported orgasms are genital orgasms caused by nipple stimulation, and may be directly linked to the genital sensory cortex ("the genital area of the brain"). *

In business

Some companies and non-profit organisations have used the word ''nipple'' or images of nipples to draw attention to their product or cause.

Etymology

The word "nipple" most likely originates as a diminutive of ''neb'', an

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th c ...

word meaning "beak", "nose", or "face", and which is of Germanic origin. The words "teat" and "tit" share a Germanic ancestor. The second of the two, tit, was inherited directly from Proto-Germanic, while the first entered English via

Old French Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intellig ...

References

Citations

General bibliography

* * * * * *

External links

* * {{Authority control Breast Breastfeeding Embryology Exocrine system Glands Human sexuality Mammal anatomy Midwifery Secondary sexual characteristics