A supernumerary nipple, also known as polythelia or an accessory nipple, is an extra nipple that develops on the body. This common, usually harmless congenital variation originates during early embryonic development. Around the fourth week of gestation, two thickened lines of tissue, called the mammary ridges or “milk lines,” form. A failure of this tissue to fully regress can result in the presence of extra nipple tissue at birth.
Common Visual Traits
Extra nipples can present in a wide variety of appearances, often making them difficult to distinguish from common skin lesions. Most frequently, an accessory nipple is much smaller than a typical nipple, sometimes appearing as little more than a small freckle, mole, or a slightly raised, pigmented spot. The size can range significantly, from a tiny brown papule to a structure nearly indistinguishable from a fully formed nipple and areola.
These structures frequently exhibit darker pigmentation than the surrounding skin, leading to them being mistaken for a birthmark or a melanocytic nevus. The texture may be slightly ridged, and the center may feature a small dimple or be slightly elevated off the skin surface. The color typically varies from pink to light or dark brown.
Most supernumerary nipples lack the underlying ductal structure of a normal breast. However, if the extra tissue contains glandular elements, it can react to hormonal changes in the body. In such cases, the structure may swell, become tender during menstruation or pregnancy, increase in size, or even produce a small amount of milk.
The Classification of Accessory Nipples
Medical professionals use a classification system to categorize the wide spectrum of appearances seen in accessory nipples, which helps standardize identification and management. This system organizes the structures based on the presence or absence of a nipple, areola, and underlying glandular tissue. The classification includes eight distinct grades, ranging from a complete extra breast to merely a patch of hair.
The most common types involve incomplete structures that are easily missed or mistaken for other skin features. For instance, one type is defined by the presence of a nipple alone without an areola or glandular tissue. Another common presentation is a patch of pigmented skin (the areola) with no nipple or glandular tissue present.
The simplest form may be just a patch of hair with no nipple or areola present. Conversely, the rare occurrence of a complete accessory breast contains a nipple, an areola, and functional glandular tissue. This systematic grading is helpful because the complexity of the tissue dictates how it might behave with hormonal changes.
Where Extra Nipples Typically Appear
Accessory nipples almost always form along a specific anatomical path known as the embryonic milk line, or mammary ridge. This line runs vertically down the front of the body, beginning near the armpit and extending down toward the groin area. While the vast majority occur along this line, roughly 5% are found outside this path, in an ectopic location such as the back, neck, or thigh.
The most frequent location for these structures is the region just below the normal breast, accounting for 60% to 70% of all cases. This positioning makes them often appear as a lower, smaller version of the main nipple. The presence of extra nipples is common, found in an estimated 1% to 6% of the general population.
Medical Significance and Associated Concerns
For most individuals, the presence of an extra nipple is a benign and isolated finding that poses no health risk. Because the structure may contain glandular tissue, it carries the same, albeit very low, risk of developing the same diseases that affect normal breast tissue. In rare instances, benign conditions like fibroadenomas or even cancerous changes could theoretically occur, though this is not a common concern.
There has been historical debate regarding an association between supernumerary nipples and certain congenital abnormalities, particularly those affecting the renal or urinary tract systems. While some older studies suggested a notable link, more recent investigations have largely weakened this association, especially in otherwise healthy individuals. A thorough medical workup for other malformations is generally not necessary unless the patient presents with additional symptoms or other minor physical abnormalities.
Individuals who find their accessory nipple cosmetically undesirable or experience discomfort or leakage due to hormonal sensitivity may elect to have it removed. The procedure is typically a minor surgical excision performed under local anesthetic. Removal is generally straightforward, resulting in a small, fine-line scar that resolves aesthetic or physical concerns.