The appearance of an extra nipple, medically known as a supernumerary nipple or polythelia, is a common congenital variation in human anatomy. While the tissue is always present from birth, its visibility can change significantly throughout a person’s life, leading many to wonder if such a structure can develop or be newly noticed in adulthood. This article explores the biological origins of this anomaly and details the specific circumstances under which it may seem to appear long after infancy.
Defining and Classifying Supernumerary Nipples
A supernumerary nipple is an accessory structure consisting of extra nipple or associated breast tissue, distinct from the two typical nipples. The prevalence of this minor congenital anomaly is estimated to be between 1% and 6% of the general population. To standardize clinical description, accessory breast tissue is categorized using the Kajava classification system, which includes eight types. These types range from Type I, a complete accessory breast with glandular tissue, areola, and nipple, to Type VI, which is a nipple structure only, to Type VIII, which is only a patch of hair. The most common presentation is Type VI, which is a small, solitary nipple structure often mistaken for a mole or a freckle.
The Embryonic Origin of Extra Nipples
Supernumerary nipples originate during the early stages of fetal development, specifically around the fourth week of embryogenesis. At this time, thickened ectodermal strips, known as the mammary ridges or “milk lines,” form bilaterally along the torso. These lines extend from the armpit region down toward the groin area. In typical development, most of this thickened tissue regresses, remaining only in the pectoral area where the main breasts will form. A supernumerary nipple results from the incomplete regression of the mammary ridge elsewhere along this line, leaving behind a remnant of mammary tissue.
Visibility and Timing of Appearance
The tissue is present at birth, but its small size and lack of pigmentation often render it unnoticeable in infancy and childhood. The anomaly is not newly formed later in life but becomes activated and visible by hormonal shifts.
The first major period of change is puberty, where increased circulating estrogen and progesterone stimulate the previously dormant tissue. This hormonal influence may cause the structure to increase in size, darken in color, or become slightly elevated. For women, the accessory nipple may also become tender or swell cyclically during the menstrual phase, mirroring the behavior of the normal breast.
The most dramatic manifestation occurs during pregnancy and lactation, when hormone levels peak. If the supernumerary nipple contains functional glandular tissue (Polymastia or Type I), it may experience significant swelling and tenderness. In rare cases, this accessory breast tissue can even produce and secrete milk, a phenomenon known as lactation.
Health Implications and Clinical Diagnosis
For most individuals, a supernumerary nipple is a benign finding that requires no medical intervention. Because this structure is composed of mammary tissue, it is susceptible to the same physiological changes and diseases as the primary breasts. The tissue has the potential to develop cysts, inflammation, or, very rarely, malignant tumors.
There has been historical debate regarding a potential association between supernumerary nipples and underlying internal anomalies, particularly those affecting the kidneys or urinary tract. Current medical consensus suggests that for an isolated supernumerary nipple, this link is weak and often disputed.
A diagnosis is typically made through simple visual inspection and physical examination. If the lesion is unusually large or needs to be differentiated from a mole or other skin growth, a biopsy may be performed. If the accessory nipple is cosmetically bothersome or causes physical symptoms, surgical removal is a straightforward treatment option. Otherwise, the recommendation is to monitor the structure and report any significant changes to a healthcare provider.