Nipple

Contents

1. Overview
2. Etymology
3. Cultural Impact

This article delves into the anatomy of the nipple, a distinct projection on the breast. It’s crucial to distinguish this from other uses, for which one might consult Nipple (disambiguation) .

Part of the breast

The nipple, along with the areola and the breast itself, forms a key anatomical unit. Anatomically, it’s designated in Latin as papilla mammaria. Within medical classification systems, it’s found under MeSH identifier D009558, TA98 code A16.0.02.004, TA2 code 7105, and is recognized in the Foundational Model of Anatomy as FMA 67771. The broader field of anatomical terminology also categorizes it.

The nipple, a prominent protrusion on the surface of the breast , serves a vital function in lactating females. It acts as the exit point for milk produced by the mammary gland . This milk travels through the lactiferous ducts and is delivered to an infant during nursing . The expulsion of milk can occur passively, or it can be actively ejected through the contraction of smooth muscle fibers integrated within the ductal system. Encircling the nipple is the areola , a pigmented area that typically exhibits a darker hue than the surrounding skin.

While most prominent in females, male mammals also possess nipples, though they generally lack the same functional significance or pronounced appearance. In non-human animals, the term teat is more commonly used. The word “nipple” can also refer to the artificial, flexible mouthpiece found on a baby bottle .

In humans, both male and female nipples are capable of being sexually stimulated and can play a role in sexual arousal . Across various cultures, female nipples have often been sexualized , sometimes viewed as sex objects and subjected to evaluation based on their physical characteristics and perceived sex appeal.

Etymology

The word “nipple” is believed to derive from a diminutive form of “neb,” an Old English word of Germanic origin . This root word conveyed meanings such as “beak,” “nose,” or “face.” The terms “teat” and “tit” share a common Germanic ancestor. “Tit” was directly inherited from Proto-Germanic, while “teat” entered the English language via Old French .

Structure

The breast is a complex organ, and a cross-section reveals the arrangement of its components, including the mammary gland , lobules , fatty tissue , and skin . Key structures within this are the nipple and the areola , connected by the milk duct . The nipple itself is situated anteriorly, overlying the pectoralis muscles and the chest wall .

In mammals , the nipple, also referred to as the mammary papilla or teat , is a small projection of skin . It houses the openings of 15 to 20 lactiferous ducts , which are arranged in a cylindrical fashion around the tip. Marsupials and eutherian mammals typically display an even number of nipples, arranged bilaterally, with the count ranging from as few as two to as many as nineteen.

The skin of the nipple is densely innervated with specialized nerves that are highly sensitive to various stimuli. These include both slowly-adapting and rapidly-adapting cutaneous mechanoreceptors . Specifically, Type I slowly-adapting receptors are associated with multiple Merkel corpuscle end-organs , while Type II slowly-adapting receptors are linked to single Ruffini corpuscle end-organs . Similarly, Type I rapidly-adapting receptors are characterized by multiple Meissner corpuscle end-organs , and Type II rapidly-adapting receptors by single Pacinian corpuscle end-organs . The primary nerve supply to the nipple originates from the lateral cutaneous branches of the fourth intercostal nerve . Furthermore, the nipple serves as a critical anatomical landmark, demarcating the T4 (fourth thoracic vertebra) dermatome and generally resting at the approximate level of the diaphragm.

The arterial supply to the nipple and the entire breast originates from several sources: the anterior intercostal branches of the internal thoracic (mammary) arteries, the lateral thoracic artery, and the thoracodorsal arteries. The venous drainage follows a parallel course to the arterial supply. The lymphatic drainage system of the nipple is identical to that of the breast. Approximately 75% of the lymph is channeled through the axillary lymph nodes, located near the armpit. The remaining lymph drainage exits the nipple and breast via the infroclavicular, pectoral, or parasternal nodes.

It is worth noting that the anatomy of the nipple undergoes changes throughout the lifespan of both males and females. These modifications are often considered normal developmental or age-related processes.

In male mammals

Nearly all mammals possess nipples. The evolutionary reasons behind the presence of nipples in males have been a subject of ongoing scientific inquiry. Sexual dimorphism , the distinct differences between sexes within a species, is generally attributed by evolutionary biologists to the pressures of sexual selection . The prevailing scientific consensus suggests that the male nipple persists because there is no significant evolutionary disadvantage to its retention. In this context, some biologists might categorize the male nipple as a spandrel —a trait that arises as a byproduct of other evolutionary developments rather than being directly selected for.

In humans, male nipples are frequently surrounded by body hair .

Function

The primary physiological purpose of nipples, particularly in females, is the delivery of milk produced by the mammary glands during lactation to an infant . The act of breastfeeding involves nipple stimulation by the infant, which triggers the release of oxytocin from the hypothalamus . Oxytocin is a crucial hormone that increases in levels during pregnancy and acts upon the breast to facilitate the milk-ejection reflex , commonly known as the “let-down” reflex. The release of oxytocin, stimulated by the infant’s suckling, also causes the uterus to contract, a process that continues even after childbirth. These strong uterine contractions are vital for preventing excessive bleeding, or post-partum haemorrhage , by constricting the uterine arteries.

When an infant suckles or otherwise stimulates the nipple, oxytocin levels rise, leading to contractions of small muscles within the breast. These contractions propel milk through the milk ducts and towards the nipple. This process, facilitated by nipple stimulation, is essential for moving breast milk out of the ducts and to the nipple. A successful latch is when the infant securely attaches to the nipple, with the lower portion of the areola entering the infant’s mouth. A suboptimal latch, where the infant grasps too close to the nipple tip, can result in insufficient nipple stimulation to elicit the let-down reflex. Such poor attachment can lead to discomfort, sore and cracked nipples , and may even discourage the mother from continuing to breastfeed. The volume of milk produced is also responsive to nipple stimulation; increased nursing time by the infant signals the mammary glands to enhance milk production.

A silicone teat or nipple is commonly used for bottle feeding .

Clinical significance

Pain

Nipple pain can significantly deter women from breastfeeding. Sore nipples that progress to cracking are a serious concern, as the associated pain often leads women to cease breastfeeding. In severe cases, an ulcer may form on the nipple. A primary cause of sore and cracked nipples is an incorrect latch by the infant. If a nipple appears flattened or “wedge-shaped,” it often indicates a poor attachment, increasing the risk of nipple damage. Herpes infections of the nipple can also be extremely painful. Excessive friction from clothing against the nipple can lead to a fissure , causing pain.

Discharge

Nipple discharge refers to any fluid that seeps from the nipple of the breast. While it is not expected in lactating women, discharge in non-pregnant or non-breastfeeding women may not always be cause for alarm. However, nipple discharge in men is considered atypical and may indicate an underlying issue. The discharge can occur spontaneously or only upon squeezing the nipple. It may be unilateral or bilateral, and its characteristics can vary widely: it can be clear, green, bloody, brown, or straw-colored, and its consistency can range from thick and sticky to thin and watery.

In some instances, nipple discharge may resolve on its own without medical intervention. While most cases of nipple discharge are benign (not cancerous), there is a rare possibility that it could be an early sign of breast cancer. Therefore, it is crucial to identify the underlying cause and seek appropriate treatment. Common reasons for nipple discharge include:

Pregnancy
Recent breastfeeding
Friction from clothing, such as a bra or T-shirt
Injury to the breast
Infection
Inflammation and clogging of the breast ducts
Noncancerous pituitary tumors
Small growths within the breast, which are usually benign
Severe underactive thyroid gland (hypothyroidism )
Fibrocystic breast changes, characterized by normal lumpiness in the breast
The use of certain medications
The use of certain herbs, such as anise and fennel
Duct ectasia of the breast , a widening of the milk ducts

Occasionally, infants may exhibit nipple discharge, which is typically caused by maternal hormones transferred before birth and usually resolves within two weeks. Cancers, such as Paget’s disease , a rare malignancy affecting the skin of the nipple, can also manifest as nipple discharge.

Nipple discharge that is considered abnormal typically presents as bloody, originates from only one nipple, or occurs spontaneously without any squeezing or manipulation. Discharge is more likely to be normal if it emanates from both nipples or only appears when the nipples are squeezed. Squeezing the nipple to investigate discharge can sometimes exacerbate the situation, and leaving it undisturbed may allow the discharge to cease.

Nipple discharge in males generally warrants greater concern. Diagnostic procedures often include a mammogram and an examination of the discharged fluid. A biopsy is frequently performed, with fine needle aspiration (FNA) being a relatively quick and less painful option. This involves using a very thin, hollow needle with slight suction to obtain a small tissue sample from beneath the nipple. A local anesthetic may not be necessary due to the thinness of the needle, and the injection itself might be more uncomfortable than the biopsy procedure.

Some men develop gynecomastia , a condition characterized by the development and growth of breast tissue beneath the nipple. This can be accompanied by nipple discharge. Swelling of the nipple in males may also occur, potentially due to elevated estrogen levels.

Appearance

Prior to puberty , the nipples of girls and boys are largely similar in appearance. Changes in nipple appearance can be either normal or indicative of an underlying medical condition.

Inverted nipples : This is considered normal if the nipples have always been indented inward and can be easily everted upon touch. However, if the inversion is a new development, it constitutes an unexpected change.
Skin puckering of the nipple: This can result from scar tissue, often due to surgery or infection, though it can also form without a discernible cause. Most cases do not require treatment. However, puckering or retraction of the nipple can be a concerning sign, potentially indicating an underlying change in the breast tissue that might be cancerous.
Warm, red, or painful nipple: These symptoms can suggest an infection, though they are rarely associated with breast cancer.
Scaly, flaking, or itchy nipple: This is most commonly attributed to eczema or a bacterial or fungal infection. If this is a new symptom, it is unexpected. Persistent scaling, flaking, or itching of the nipple can, in rare instances, be a sign of Paget’s disease.
Thickened skin with large pores (peau d’orange): This appearance, resembling an orange peel, can indicate an infection within the breast or inflammatory breast cancer. This is not an expected change.
Retracted nipples: This occurs when a nipple that was previously protruding begins to pull inward and fails to emerge even when stimulated.

The average projection and size of human female nipples is reported to be slightly over 9.5 mm (3/8 inch).

Breast cancer

Changes in the nipple and areola are often among the earliest indicators of breast cancer , although symptoms can vary among individuals, and some may experience no noticeable signs. In some cases, breast cancer is discovered during a routine mammogram .

Potential warning signs include:

A new lump in the nipple, breast, or armpit.
Thickening or swelling of any part of the breast, areola, or nipple.
Irritation or dimpling of the breast skin.
Redness or flaky skin in the nipple area or on the breast.
Retraction of the nipple or pain in the nipple area.
Nipple discharge other than breast milk, including blood.
Any alteration in the size or shape of the breast or nipple.
Pain in any region of the breast.

It is important to remember that changes in the nipple are not always indicative of breast cancer. Other nipple conditions can present with symptoms that mimic those of breast cancer.

Vertical transmission

Certain infections can be transmitted through the nipple, particularly if the nipple is irritated or injured. In such cases, the nipple can become infected with Candida , a fungus commonly present in the mouth of breastfeeding infants. The infant can then transmit the infection to the mother. While this infection is often localized to the nipple area, it can, in some instances, progress to a more severe breast infection, known as mastitis . If the mother has an infection without any cracks or ulcerations on the nipple, breastfeeding may still be safe for the infant.

Herpes infection of the nipple can be insidious, with small lesions that are typically intensely painful. Herpes infection in newborns is a serious and potentially fatal condition. Transmission of Hepatitis C and B to an infant can occur if the nipples are cracked. Other infections can also be transmitted through breaks in the nipple’s skin, potentially infecting the infant.

Other disorders

A variety of other conditions can affect the nipple, including:

Nipple bleb
Candida infection of the nipple
Eczema of the nipple
Inverted nipple
Staphylococcus infection of the nipple
Edematous areola
Herpes infection of the nipple
Raynaud’s phenomenon of the nipple
Flat nipple

Surgery

A nipple-sparing mastectomy , also known as a subcutaneous mastectomy, is a surgical procedure where the breast tissue is removed while preserving the nipple and areola. Historically, this procedure was primarily performed prophylactically or for benign breast conditions due to concerns about cancer developing in the retained ductal tissue within the areola. However, recent studies suggest that it can be an oncologically safe procedure for tumors that are not located in the subareolar region.

Society and culture

The cultural practice of concealing the female nipple under clothing has been prevalent in Western culture since the 19th century. The female nipple’s perception as an intimate part may have roots in Victorian morality , similar to the practice of riding side-saddle. The exposure of the entire breast and nipple can be a form of protest for some and a legal offense for others. Generally, the exposure of nipples is considered immodest and, in certain contexts, may be viewed as lewd or indecent behavior.

A notable legal case in Erie, Pennsylvania, concerning the public exposure of breasts and nipples, reached the United States Supreme Court . The ordinance in question regulated public nipple exposure, defining public indecency as appearing in a state of nudity, further elaborated to include an uncovered female nipple. Crucially, the regulation did not apply to male nipple exposure. This disparity has been highlighted, noting that a man displaying his bare chest might face social repercussions like being denied service in restaurants, whereas a woman exposing her nipples could be legally treated the same as someone engaging in public sexual acts. This distinction is permissible under US law.

The legal landscape surrounding nipple exposure varies significantly across the United States. Some states prohibit the visibility of any part of the breast, while others restrict female chest anatomy by banning exposure of structures below the top of the areola or nipple. For instance, West Virginia and Massachusetts have specific regulations. West Virginia’s law clearly states that the display of “any portion of the cleavage of the human female breast exhibited by a dress, blouse, skirt, leotard, bathing suit, or other wearing apparel [is permitted] provided the areola is not exposed, in whole or in part.'”

Social media platforms also grapple with policies regarding nipple exposure. Instagram , for example, maintains a “no nipples” policy, with exceptions for images of post-mastectomy scarring and women actively breastfeeding. Nudity in artistic representations, such as paintings and sculptures, is generally permitted. Previously, Instagram had removed images of nursing mothers and faced backlash, notably when it removed images of Rihanna and suspended her account in 2014 for posting selfies that included nipples. This incident spurred the Twitter campaign #FreeTheNipple . In 2016, the Instagram account @genderless_nipples encouraged users to post images of nipples from both sexes, showcasing close-ups of male and female nipples to draw attention to perceived inconsistencies in policy enforcement. Some users have found ways to circumvent these restrictions. Facebook has also encountered challenges in defining and consistently applying its own nipple policy.

Filmmaker Lina Esco created a film titled Free the Nipple , which critiques laws and restrictions that target female toplessness or images of female nipples while exempting male nipples, framing it as an instance of societal sexism .

A portrait by Joseph Duplessis of Marie Thérèse Louise of Savoy from the 18th century subtly reveals a nipple.
A Namibian woman is depicted going topless .

Sexuality

Nipples are highly sensitive to touch, and nipple stimulation can be a potent trigger for sexual arousal . While relatively few women report experiencing orgasm solely from nipple stimulation, research has begun to illuminate the neurological pathways involved. Prior to the 2011 functional magnetic resonance imaging (fMRI ) study by Komisaruk and colleagues, reports of women achieving orgasm through nipple stimulation were largely based on anecdotal evidence . Komisaruk’s groundbreaking study was the first to map the sensory regions of the brain, revealing that sensations originating from the nipples travel to the same areas that process sensations from the vagina, clitoris, and cervix. This suggests that nipple-induced orgasms may be directly linked to the genital sensory cortex, the part of the brain associated with genital sensation.

Piercings

A nipple piercing is a form of body piercing that typically centers on the base of the nipple. While piercings can be placed at various angles, horizontal and vertical orientations are most common. It is also possible to have multiple piercings stacked one above the other.

In business

Some companies and non-profit organizations have strategically employed the word “nipple” or images of nipples to capture attention for their products or causes.