Nipples of the mammary glands: anatomy and functions

The nipple and areola form a single nipple-areolar complex. Milk ducts converge within the nipple, opening onto its surface through several orifices. The surrounding smooth muscle fibers and a rich network of nerve endings make the area very sensitive. [1]

Milk ducts and their terminal sections are organized to ensure milk transport during lactation and respond to hormonal signals. Nipple stimulation triggers neurohormonal mechanisms that influence the release of prolactin and oxytocin and, consequently, the maintenance of milk production and secretion. [2]

The areola contains specialized sebaceous glands known as Montgomery glands. These secrete a lipid secretion that helps protect the skin of the nipple and areola from drying out and microdamage, especially during pregnancy and breastfeeding. The secretion has also been described as having "signaling" properties that help the newborn locate the breast. [3]

The shape and protrusion of the nipple change with temperature, touch, and arousal due to smooth muscle contraction. This is a normal physiological response and is not, in itself, a sign of disease. [4]

Table 1. The main elements of the nipple-areolar complex and their role

Element	What is this	Practical significance
Nipple	The protruding part with the openings of the milk ducts, nerves and smooth muscles	Participation in feeding, high sensitivity, reaction to cold and stimulation
Areola	Pigmented area around the nipple	Protection, a guide for the baby during feeding, the location of the Montgomery glands
Montgomery glands	Sebaceous glands of the areola	Lubrication and protection of the skin, more noticeable during pregnancy and lactation
Milk ducts	Milk-conducting ducts	May be a source of some types of discharge and inflammation
Skin and epidermis	Thin, easily irritated	Vulnerability to dermatitis, cracks, infections

[5]

Normal variations: shape, size, pigmentation, "retraction"

Nipples vary in size, height, symmetry, and color among individuals. Small or large areolas, varying pigmentation, and moderate asymmetry are often individual characteristics. [6]

A flat nipple doesn't always interfere with breastfeeding: what's more important is the baby's ability to latch on not only to the nipple but also to part of the areola. Problems most often arise with severe inversion or with pain and cracks, which impair latching and trigger a "vicious cycle" of injury. [7]

Inverted nipples can be congenital or acquired. Congenital inversion is often bilateral and stable for years, whereas sudden inversion, particularly on one side, requires evaluation of the underlying causes, including inflammatory and neoplastic processes. [8]

Sometimes, accessory nipples are found along the "milk line." This is usually a benign anatomical feature, but any new nodules, ulcers, bloody discharge, or persistent skin changes in the nipple area require examination. [9]

Table 2. Nipple shapes and what is important to evaluate

Option	What does it look like?	What is important
Speaker	The nipple is noticeably elevated	Usually normal
Flat	Almost at the level of the areola	Often this is normal, but the technique of attachment during feeding is important
Congenitally drawn in	"Hole", usually from childhood	Most often benign, but can complicate feeding
Drawn in acquired	The retraction appeared recently.	Requires diagnosis, especially if unilateral
Asymmetry	The sides are different	Often this is the norm, but new changes are assessed separately

[10]

How nipples change with age and throughout life

During puberty, hormones cause glandular tissue to grow and the pigmentation of the areola to change. During this time, temporary sensitivity, mild soreness, and fluctuations in nipple size are possible, especially during cyclical changes.

During pregnancy, the areola often darkens, and the Montgomery glands become more visible. This is thought to be an adaptation to future lactation: the skin prepares for frequent mechanical stress and increased humidity, and the glands' secretions help reduce dryness. [12]

In breastfeeding, supply and demand are key: regular breast drainage and nipple stimulation support milk production through prolactin, while oxytocin promotes milk release through contraction of myoepithelial cells. Against this background, nipples may become more sensitive, especially in the first weeks, until feeding technique has become stable. [13]

As we age, the ratio of glandular to fatty tissue changes, skin becomes drier, and its elasticity decreases. This can increase susceptibility to irritation and microcracks, so skin care and attention to new symptoms become more important.

Table 3. Typical changes in the nipple and areola at different periods

Period	Frequent physiological changes	When is the best time to see a doctor?
Adolescence	Growth, pigmentation, episodic sensitivity	Compaction, discharge, ulcers, pronounced unilateral asymmetry
Pregnancy	Darkening of the areola, prominent Montgomery glands	Bloody discharge, ulcers, persistent nipple eczema
Lactation	Increased sensitivity, risk of cracks	Fever, severe pain, increasing redness, purulent discharge
Menopause and older age	Dry skin, irritation, changes in elasticity	New nipple retraction, unilateral discharge, non-healing skin changes

[15]

Common benign nipple problems: why they occur and what they look like

The most common cause of pain and cracks during breastfeeding is mechanical trauma due to improper breastfeeding. Cracks increase the risk of skin infection and intensify pain, which can lead to poor latching and further trauma. [16]

The second major cause is dermatological conditions: contact dermatitis from cosmetics, detergents, breast pads, and fabric friction, as well as atopic dermatitis. Redness, itching, dryness, and flaking are typical of the nipple; if the symptoms are unclear, a more precise diagnosis is sometimes required, as nipple eczema has a wide range of causes. [17]

During lactation, candidal lesions and other skin infections are possible, mimicking the "burning" sensation and pain that sometimes persists after feeding. Clinical guidelines emphasize the importance of differentiating infection from mechanical trauma and vasospasm, as treatment strategies vary. [18]

Montgomery glands sometimes become inflamed or clogged, appearing as small, painful bumps on the areola. In most cases, gentle care and avoiding irritants helps, but attempts to "squeeze" the contents increase the risk of bacterial infection. [19]

Table 4. Common causes of nipple pain and injury and basic steps

Cause	Typical signs	First measures
Incorrect attachment	Cracks, pain at the beginning of feeding, bleeding	Correction of technique, early referral to a lactation consultant
Contact dermatitis	Itching, redness, flaking	Remove the irritant, gentle care, assess the need for local therapy
Candidiasis and other infections	Burning, pain after feeding, cracks	Clinical assessment, treatment according to indications, exclusion of confounding causes
Montgomery's gland inflammation	Painful lump on the areola	Do not squeeze, maintain careful hygiene, observe, and examine if the condition worsens.
Vasospasm of the nipple	Pallor then pain, associated with cold	Warmth, protection from cold, assessment of associated factors

[20]

Nipple discharge: what types are there and how are they different?

Nipple discharge is often benign, but the type of discharge is crucial. Important characteristics include whether the discharge occurs on its own, on one or both sides, from one duct or several, and whether it is colored or contains blood. [21]

Physiological discharge is usually bilateral, from multiple ducts, and occurs when the areola is compressed. This can occur with hormonal fluctuations, nipple stimulation, and endocrine causes, such as hyperprolactinemia; this condition is often described as galactorrhea if the discharge is milky outside of pregnancy and lactation. [22]

Spontaneous, unilateral, and bloody discharge from a single duct are most often considered pathological. In such situations, diagnostic testing is usually required, as the cause may be either benign ductal changes or tumors. [23]

The examination algorithm depends on age, associated symptoms, and examination results. Modern reviews emphasize the role of imaging: ultrasound and mammography as initial methods, and magnetic resonance imaging in cases of persistent suspicion and negative initial studies. [24]

Table 5. Type of discharge and typical assessment tactics

Nature of discharge	It happens more often when	What do they usually do?
Bilateral, from several ducts, with compression	Physiology, endocrine causes	Evaluation of drugs and hormones according to indications, observation
Dairy outside of pregnancy and lactation	Galactorrhea, hyperprolactinemia, hypothyroidism, medications	Prolactin, thyroid hormones, assessment of causes
Spontaneous, unilateral, from one duct	Pathology of the duct, sometimes a tumor	Examination, visualization, further examination based on the results
Serous or bloody	Intraductal processes, including rare tumors	Diagnosis without delay, exclusion of the oncological process

[25]

Skin changes of the nipple: dermatitis, infection, or Paget's disease

Nipple dermatitis most often presents with itching, dryness, flaking, and redness, often affecting both sides and associated with an irritant or atopy. However, the appearance can mimic other conditions, so if the condition persists, it's important not to self-medicate. [26]

Paget's disease of the nipple is a rare form of breast cancer that often looks like "nipple eczema" but has its own telltale signs: persistent skin changes specifically on the nipple, often one-sided, possibly oozing, crusting, burning, flattening or retraction of the nipple, and discharge, sometimes bloody. [27]

Key principle: If nipple eczema does not resolve with adequate treatment within a reasonable timeframe or is unilateral and prone to progression, clinical evaluation and often biopsy are required to exclude Paget's disease. Reviews emphasize that tissue verification may be necessary in cases of diagnostic uncertainty. [28]

Also alarming are the following combinations: skin changes plus a lump in the breast, enlarged axillary lymph nodes, breast deformity, ulcers, or a recently developed indentation. This does not automatically indicate cancer, but it does indicate the need for immediate examination. [29]

Table 6. How to differentiate common causes of nipple rash based on clinical clues

State	Most often affects	Typical signs	What confirms the diagnosis?
Contact or atopic dermatitis	Often both sides	Itching, dryness, flaking, connection with an irritant	Examination, response to trigger removal and therapy
Skin infection, including candidiasis	Often during lactation	Burning, soreness, cracks, sometimes pain after feeding	Clinical presentation, response to treatment, exclusion of other causes
Paget's disease	Most often 1 side	Persistent "eczema" of the nipple, crusting, oozing, possible discharge	Breast biopsy and examination
Inflammation of the ducts and mastitis	Often during lactation	Pain, redness, local warmth, sometimes fever	Examination, sometimes ultrasound
Vascular reactions, vasospasm	Often in cold weather	Pallor, then pain, associated with temperature	Typical picture, ruling out cracks and infection

[30]

Diagnosis and treatment: what is usually done in practice

They begin with an examination and clarification of symptoms: when the changes appeared, whether there is pain, itching, cracks, discharge, fever, hardening, one-sidedness, and whether the process is related to lactation and contact with irritants. This determines whether an urgent examination is required or whether adjustments to care and observation are sufficient. [31]

When abnormal discharge or tumor is suspected, imaging is typically used. Current reviews describe mammography and ultrasound as the basis for initial evaluation, and magnetic resonance imaging as a method for clarifying the cause when suspicion persists and initial tests are negative. [32]

For pain and inflammation during lactation, the approach is increasingly described as a "mastitis spectrum": from congestion and inflammation to bacterial mastitis and abscess. The updated mastitis protocol emphasizes the importance of correcting the underlying causes, careful management, and the rational use of antibiotics when truly indicated. [33]

Home remedies are generally safe unless there are any red flags: gentle hygiene, avoiding irritants, proper feeding technique, treating cracks, and pain management in consultation with a doctor. However, persistent skin changes in the nipple, bloody discharge, rapidly developing inversion, a lump in the breast, or systemic symptoms require an in-person evaluation. [34]

Table 7. Symptoms that require immediate medical attention

Symptom	Why is it important?	What do they usually do?
Bloody or serous discharge, especially one-sided and spontaneous	Pathology of the duct is possible; an oncological process must be excluded.	Examination, visualization, additional examination as indicated
New nipple inversion on 1 side	Sometimes associated with tumor or inflammation	Clinical evaluation and imaging
Persistent nipple eczema that won't go away	Paget's disease must be ruled out	Examination, biopsy as indicated
Breast lump plus nipple changes	Increases the significance of symptoms	Inspection, visualization, routing
Fever, rapid increase in redness and pain during lactation	Risk of mastitis and abscess	Assessment, treatment according to protocols, sometimes drainage

[35]

Conclusions

Nipples and areolas vary greatly, and many features of shape and color are normal. In clinical practice, the "nipple type" is not as important as the dynamics: what has changed recently, on which side, and whether there is pain, discharge, or persistent skin signs. [36]

The most alarming signs include unilateral spontaneous discharge, new indentation, non-healing skin changes on the nipple, and a breast lump. These symptoms warrant imaging and, if necessary, biopsy. [37]