Nipples – Structure, Functions and Diseases

The nipple is a conical or cylindrical protrusion located at the apex of the breast . This structure represents the point where the glandular ducts (or galactophores) converge, to open to the external surface of the body.
The nipple is hyperpigmented and has a soft and supple texture. At its top, this has a wrinkled appearance, due to the presence of the small outlet orifices of the milk ducts . The latter transport the milk produced by the mammary gland to the outside .
Compared to the cutaneous plane, the nipple is more or less raised. Occasionally, this can be retracted below the skin surface, but, when stimulated, it ejects upwards and outwards. When it remains permanently inverted, on the other hand, we speak of inversion of the nipple ; this condition is abnormal and must be checked from a medical point of view.

The nipple can be the site of various pathological processes, including malformations, infections, traumas and neoplasms.


The breast is an organ made up of glandular tissue (organized into lobules), a series of ducts (which carry milk to the nipple) and a part of fatty tissue .
At the apex of the breast, there is the nipple , that is a conical or cylindrical relief, more or less protruding and pigmented (generally dark pink or brown in color).

Usually, this structure is located at the level of the fourth intercostal space, on the mid-clavicular line (ie slightly below the middle of the chest), but the position is inconstant, as the breasts are pendulous.
The size of the nipple is usually proportional to that of the breast: the relief has an average height of 10-12 mm and a diameter of 9-10 mm.
The skin that covers it is corrugated ( area cribrosa ) by dimples and papillae, in which 15-20 milk ducts open; in fact, on its surface, the small outlet orifices can be observed.

The nipple also contains smooth muscle tissue , arranged circularly and radially, and responsible for its erection .
The nipple is surrounded by the mammary areola , that is, by a circular area of ​​hairless skin (a couple of centimeters in diameter). The latter contains the Montgomery glands (important for making the nipple soft and elastic during breastfeeding ), and sometimes also the accessory breast tissue, which becomes evident with the milky secretion .

Development and functions

  • During the first years of life, the nipple is small in size. Upon reaching puberty, this structure increases in volume particularly in women, while it remains “rudimentary” in men. During pregnancy and breastfeeding, the nipple reaches its maximum development, becoming more prominent and pigmented.
  • Under the influence of direct or reflex stimuli, the nipple goes into erection, lengthening and increasing in consistency; this phenomenon, called telotism, is due to the presence of smooth muscle cells similar to those of the areolar muscle.
  • In both men and women, the nipples also represent an erogenous zone. Their prolonged and intense stimulation during sexual activity can therefore lead to arousal.
  • The main physiological purpose of the nipples is the ejection of breast milkin the period following the birth event . This phenomenon allows the initiation of breastfeeding.

Milk is produced in the breasts by a set of acinar glands (called alveoli) and is carried to the nipples through the milk ducts. After birth, in fact, the decrease in estrogen and progesterone allows the stimulating effect of prolactin on the secretion of milk by the cells of the alveoli and allows lactation to take place.
To get milk, the infant simply sucks on the nipples (known as sucking ), causing milk to flow through the ducts.

Sucking stimulates the contraction of the myoepithelial cells that surround the alveoli and pushes the milk to flow through the milk ducts ( ejection ).

Alterations and symptoms

Inversion of the nipple

Normally, the nipples are protruding. In some cases, however, they appear inverted, therefore reentering the breast, even if stimulated manually or with the cold.
Nipple inversion is often a benign condition, but it can also indicate the presence of a more severe problem. This abnormality can affect only one breast or both.
The inversion of the nipple may be present from birth (due to a congenital shortness of the milk ducts ) or acquired. In the latter case, the retraction is sustained, more often than not, by a periductal fibrosis resulting from inflammatory processesor surgery. If the nipple does not protrude, it can interfere with the normal ability to breastfeed.
Sometimes, nipple inversion can be the first sign of breast cancer , especially when it is asymmetrical or associated with blood discharge or the presence of a lump .


Inversion of the nipple
Benign Malignant
·                                 Symmetrical

·                                 Similar to a crack

·                                 Asymmetrical

·                                 Distorting the nipple, which appears deviated to one side

Nipple discharge

In some cases, a small amount of clear or yellow, white, or green liquid may be squeezed out of the ducts in response to breast manipulation or spontaneously . This manifestation can occur in males or in women, outside the period of pregnancy and breastfeeding .
The serum secretion may be an abnormal symptom or harmless; a blood loss from the nipple (at a microscopic and macroscopic level) is never, however, to be considered normal.
For this reason, the causes of these secretions must be investigated. The most serious condition related to this sign is, however, breast cancer (usuallycarcinoma of the intraductal or invasive ductal type). In most cases, however, the cause is benign and attributable to pathologies of the benign mammary ducts (e.g. ductal ectasia and intraductal papilloma) or breast infections ( mastitis ).


The galactorrhea is the secretion of a milky serum, non- puerperal , from different ducts of both breasts.

Often, this phenomenon is due to a prolactin-secreting pituitary adenoma ( prolactinoma ), a hormone that at high levels stimulates the glandular tissue of the breast.
Galactorrhea can also result from hypothalamic tumors and other endocrine disorders, such as acromegaly , thyrotoxicosis , primary hypothyroidism and Cushing’s disease .

Supernumerary nipples (polythelia)

In addition to the typical location, the nipples can develop in excess, usually along two mammary lines, which run from the armpits to the groin. Polythelia is a generally sporadic condition, but it can also recognize a genetic predisposition.
Supernumerary nipples may appear as simple pigmented patches, similar to moles.


The malformations of the nipple are attributable to variations in its shape. These conditions can be detrimental to breastfeeding: the structure may be too bulky, short or even absent, making sucking more difficult.
Sometimes, instead of protruding, the nipple appears umbilicated, that is, flat or recessed in the center of the mammary areola, due to the arrest of its embryonic development .

Desquamation of the nipple

Nipple peeling is a manifestation mostly associated with dried nipple discharge. On some occasions, however, this sign can depend on an eczematous lesion . Other times, peeling of the nipple indicates the presence of Paget ‘s disease or erosive adenoma .

Main pathologies of the nipple


The fissures are small particularly painful ulcerations, which occur especially during the nursing period. These lesions deepen beyond the dermis and can be circular (i.e. around the implantation of the nipple on the areola) or run from the apex to the base of the nipple. This condition can favor the colonization of the milk ducts by infectious agents.
Often, nipple fissures spontaneously regress upon cessation of breastfeeding.

Paget’s disease of the nipple

The nipple Paget’s disease is a malignant tumor that arises from the proliferation of neoplastic cells of the milk ducts. Usually, the disease affects only one breast and is often associated with ductal breast cancer in situ or invasive type. The risk factors that predispose its onset are the same that make it susceptible to developing other types of breast cancer.
Paget’s disease produces visible changes in the skin of the areola-nipple complex: the skin appears red, dry, irritated or scaly (the appearance is similar to that of a psoriatic plaque or eczema). In about half of all cases, an underlying breast lump can be found on palpation . Other common symptoms of Paget’s disease are straw-colored discharge (serous or purulent ), itching and burning sensation around the nipple and breast areola. In addition, edema , nipple inversion and ulcerative-erosive lesions with crusting may occur .
Paget’s disease of the nipple can be diagnosed with a biopsy , but other medical investigations, such as mammography andmagnetic resonance .
The treatment involves surgical removal of tumors diagnosed (conservative or radical). Depending on the case, adjuvant surgery with chemotherapy drugs , radiotherapy, or hormone therapy may also be recommended , in order to prevent breast cancer recurrence and destroy any remaining cancer cells.

Nipple and areola eczema

Eczema can involve areola and / or nipple to varying degrees and can be part of a generalized skin disorder. However, it can also be due to Paget’s disease of the nipple or invasion of the epidermis by intraductal breast cancer.

Viral infections

The nipple area can sometimes be involved with molluscum contagiosum (swelling with associated ulcer), herpetic lesions and warts .

Sebaceous cysts

The cysts sebaceous nipple are rarely seen. This condition manifests itself as a painless swelling in close relationship with the nipple, and communicating or not with a milk duct. Sebaceous cysts can become infected.

Traumatic injuries

One or both nipples may be affected by protracted friction from a shirt or other clothing, especially while performing a sporting activity. The people most exposed to this condition are those who practice running (hence the name “runner’s nipple”) or breastfeeding. In most cases, this trauma is associated with the presence of sweat and heat and can cause irritation, redness of the skin, soreness, dryness, or bleeding.
On the other hand, friction associated with cold can result in painful lesions, often with aspects similar to those of eczema and, sometimes, with micro- hemorrhagessimulating blood secretions from the nipple. The latter condition is found above all among cyclists.

Erosive adenoma of the nipple

Erosive adenoma is a rare condition in which the nipple appears enlarged, sometimes ulcerated and bleeding. In addition, burning or itchy pain is reported. The diagnosis of erosive adenoma is confirmed with a biopsy. The treatment does not require the removal of the entire nipple, but only the affected part.


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