A person can have three or more nipples, a condition known as a congenital anomaly of the breast. This occurrence is relatively common, affecting an estimated 0.2% to 6% of the general population globally. Having an extra nipple, often referred to as a “third nipple,” is present from birth and usually represents a harmless variation in human anatomy. The presence of this extra tissue is a direct result of an event that occurs early in embryonic development.
Defining Accessory Nipples and Breast Tissue
The medical terms for having extra mammary tissue depend on the components present in the anomaly. The term Polythelia specifically refers to the presence of an extra nipple without any underlying glandular breast tissue. Conversely, Polymastia describes the presence of complete accessory breast tissue, which includes the nipple, areola, and functional glandular tissue. These extra formations are collectively known as accessory mammary tissue.
Accessory tissue is categorized using Kajava’s classification, which divides anomalies into eight distinct types. These types range from a complete extra breast (Type I) down to just a patch of hair (Type VIII). Type VI, which is Polythelia (a nipple only), is the most frequently encountered form of accessory nipple. Understanding the classification is important because the medical significance of the anomaly is related to whether functional glandular tissue is present.
The Developmental Cause and Common Locations
The biological reason for the formation of accessory nipples stems from the process of embryonic development, specifically the formation of the “milk line” or mammary ridge. This paired ectodermal thickening runs vertically down the embryo’s torso from the armpit to the groin. In typical development, this ridge regresses completely, leaving mammary tissue only in the pectoral area to form the two primary breasts.
An accessory nipple or accessory breast forms when remnants of this mammary ridge fail to regress completely during development. This failure allows for the development of extra mammary structures anywhere along the path of the original milk line. While these anomalies can appear anywhere along this path, they are most often found below the normal nipple line or in the armpit region. In some rare instances, accessory tissue can even appear outside the milk line, on the neck, back, or thigh, referred to as ectopic tissue.
Accessory nipples often look smaller and less developed than a typical nipple, sometimes resembling a mole, a freckle, or a pigmented patch of skin. Because of their appearance, many people with Polythelia may not realize they have an extra nipple until later in life, often mistaking it for a common skin lesion. Accessory tissue can sometimes be identified by being slightly elevated or having a small central dimple.
Diagnosis and Medical Significance
If an accessory nipple or breast contains functional glandular tissue, it can respond to hormonal fluctuations just like the main breasts. This means the tissue can enlarge during puberty, swell and become tender during menstruation, and potentially lactate during pregnancy or breastfeeding. Cases have been documented where a new mother only discovered the accessory tissue when milk began dripping from what she thought was a mole or freckle.
Diagnosis typically begins with a physical examination, where a healthcare provider determines if the lesion is an accessory nipple, a mole, or another skin condition. If the structure is ambiguous or if glandular tissue is suspected, further imaging like an ultrasound or a biopsy may be used to confirm the tissue type. The presence of glandular tissue in accessory breasts means they are susceptible to the same diseases as normal breast tissue, including mastitis, cysts, and even breast cancer.
There has been a debated association between accessory nipples, particularly isolated Polythelia, and other congenital anomalies, notably those involving the urinary and cardiovascular systems. Studies have linked Polythelia to conditions such as kidney disease and congenital heart defects. However, for an otherwise healthy person with an isolated accessory nipple and no other symptoms, the risk of an underlying internal anomaly is generally considered low. Surgical removal is typically reserved for cosmetic reasons, or if the tissue causes discomfort due to swelling or lactation.