The human body is a marvel of biological development, but sometimes, it carries harmless remnants of its own embryonic journey. One of the most common variations is the supernumerary nipple, also known as an accessory nipple or a “third nipple.” Having an extra nipple is a relatively common congenital anomaly that affects millions of people worldwide. Often mistaken for a mole or a simple birthmark, a supernumerary nipple is typically a benign and medically insignificant finding. However, its appearance can be a source of curiosity, cosmetic concern, or anxiety. This comprehensive guide will demystify this common trait, explaining its origins, its variations, and the options available for those who may be concerned about it.

Supernumerary nipples commonly referred to as extra nipples or third nipples are additional nipples that develop along the “milk lines” of the body. The medical term for having an extra nipple alone is polythelia. In rarer cases, an extra nipple can be associated with underlying glandular (breast) tissue and an areola, a condition known as polymastia. Polythelia is a much more common expression.

To understand why supernumerary nipples form, it is essential to look at our earliest embryonic development. In the early weeks of gestation, a developing human embryo forms two thickened ridges of tissue on its surface called the mammary ridges, or “milk lines.” These milk lines run vertically down both sides of the body, from the armpits (axillae) to the groin.

Think of these milk lines as a temporary template for multiple pairs of nipples, similar to what is seen in mammals that have litters, like cats or dogs. In human development, this entire template is programmed to regress and disappear, except for the one spot on each side of the chest where the normal breasts will form. A supernumerary nipple is simply a harmless remnant of this embryonic milk line, a spot where one of the extra nipple buds failed to completely vanish during development. This is why the vast majority of accessory nipples are found somewhere along this path.

While many supernumerary nipples are small and may go unnoticed, they can be classified based on how much tissue is present. The Kajava classification system organizes them into several types, but for patient understanding, they can be simplified into a spectrum:

• A small patch of hair only (polythelia pilosa).
• An areola only.
• A nipple only (polythelia).
• A nipple and areola.
• A complete accessory breast with a nipple, areola, and underlying glandular tissue (polymastia).

Analogy: Imagine your body’s blueprint during development includes a line called the milk line where breast tissue can grow. Normally, just one pair of nipples develops. But sometimes, a second or even third spot along that line gets activated too, like a backup light bulb turning on.

Supernumerary nipples are caused by incomplete regression of the embryonic milk lines, which run from the armpits to the groin on both sides of the body. During fetal development, breast tissue begins forming along these lines, but normally only one pair of nipples remains, and the rest disappears.

In some people, small islands of tissue along the milk lines remain, forming supernumerary nipples. This is not due to genetics, trauma, or hormonal imbalances, though family history may play a role.

Key causes:

• Congenital anomaly – occurs during embryonic development
• Milk lines fail to fully regress
• Not associated with poor health or behavior during pregnancy

You are born with supernumerary nipples. They are not something that can be acquired or developed later in life.

Genetics and Inheritance: While most cases of supernumerary nipples appear to be sporadic, meaning they occur by chance with no other affected family members, there is a known familial tendency. The trait can be inherited, and in some families, it has been observed to be passed down in an autosomal dominant pattern. This means that a person only needs to inherit the gene for the trait from one parent to have it themselves, and they would then have a 50% chance of passing it on to each of their children.

Prevalence: Supernumerary nipples are a very common anomaly. Estimates of their prevalence vary widely, ranging from as low as 0.2% to as high as 5-6% of the population, depending on the population studied. The condition affects both males and females, though it may be noticed more frequently in females due to hormonal changes during puberty and pregnancy that can cause the accessory nipple to become more prominent or tender.

Supernumerary nipples can vary widely in appearance. Some are tiny, flat, and easily missed, while others resemble normal nipples or even include glandular tissue that behaves like breast tissue.

• Appearance: They can range from being a tiny, subtle pigmented bump, easily mistaken for a freckle or a common mole, to a fully formed structure with a distinct nipple and areola. They are often smaller and less developed than the primary nipples.
• Location: As they are remnants of the embryonic milk line, supernumerary nipples are most commonly found in a line running from the armpit down through the normal nipple and toward the abdomen. The most frequent location is on the chest, just below the normal breast. While very rare, they can occasionally appear in other locations, such as the back, shoulder, neck, or thigh.

Physical Symptoms: In the vast majority of cases, supernumerary nipples are completely asymptomatic, causing no pain or physical sensation whatsoever.

When symptoms do occur, they are typically related to the tissue’s response to hormonal fluctuations, just like normal breast tissue. These symptoms can include:

• Tenderness or Sensitivity: The accessory nipple may become tender, swollen, or more prominent around the time of puberty, during the menstrual cycle, or during pregnancy.
• Lactation: In the rare cases of polymastia where significant glandular breast tissue is present, the accessory breast can produce and leak milk during or after pregnancy (a condition known as lactorrhea).
• Irritation: A more prominent accessory nipple can sometimes become irritated from rubbing against clothing.

When to See a Doctor

Since supernumerary nipples are almost always benign, there is typically no medical need to see a doctor. However, an evaluation is recommended in the following situations:

• Diagnostic Uncertainty: If you have a lesion on your skin and are unsure if it is a mole, a skin tag, or a supernumerary nipple, a dermatologist can provide a definitive diagnosis.
• Cosmetic Concerns: If the appearance of the accessory nipple is causing psychological distress or affecting your self-confidence.
• Changes in the Lesion: Just like any skin lesion, if it changes in size, shape, or color, or if it begins to bleed or hurt, it should be examined by a doctor to rule out other problems.
• Discharge: If the accessory nipple begins to leak fluid when you are not pregnant or lactating.

Diagnosis

Diagnosis is usually made by physical examination.

• A doctor or dermatologist can usually identify it based on its characteristic appearance and its classic location along the embryonic milk line.
• A doctor may use a handheld magnifying device called a dermatoscope to get a closer look at the skin markings, which can help differentiate it from a mole.
• A skin biopsy, where a small piece of the tissue is removed and examined by a pathologist, is rarely necessary but may be performed if the diagnosis is uncertain or if there is any concern about the nature of the lesion.

Association with Other Conditions In the past, there was some belief that the presence of a supernumerary nipple could be a marker for underlying kidney or urinary tract abnormalities. However, extensive research has shown that in an otherwise healthy individual with an isolated accessory nipple, the risk of having a significant underlying anomaly is no greater than in the general population. Therefore, routine screening with tests like a kidney ultrasound is not recommended unless other signs or symptoms are present.

Management and Removal Options

Reassurance and Observation: For the vast majority of individuals, the only management needed for a supernumerary nipple is reassurance from a healthcare provider. No medical treatment is required.

Reasons for Removal: The decision to remove a supernumerary nipple is almost always elective and driven by the patient’s personal preference. The most common reasons for removal are:

• Cosmetic concerns.
• Psychological distress or embarrassment.
• Physical irritation from clothing.

In very rare cases of true polymastia (an accessory breast), removal may be considered for medical reasons. This ectopic breast tissue can, in theory, be susceptible to the same diseases as a normal breast, including benign tumors or, exceptionally rarely, breast cancer.

Removal Procedure: The standard and most effective method for removing a supernumerary nipple is a simple surgical excision.

• This is a minor procedure that is typically performed by a dermatologist or a plastic surgeon in an office setting.
• The area is numbed with a local anesthetic injection.
• The surgeon then uses a scalpel to carefully cut out the nipple and any associated tissue.
• The small wound is closed with a few stitches.
• The procedure is quick, and the recovery is straightforward. It typically results in a small, fine-line scar that is often less noticeable than the original nipple.

A supernumerary nipple is a common and fascinating remnant of our embryonic development, a harmless variation that highlights the shared mammalian blueprint from which we are built. For the vast majority of people who have them, these extra nipples are simply a unique personal trait with no medical significance, often mistaken for a common mole or birthmark. While they can sometimes cause cosmetic concern or become tender with hormonal changes, they are not a sign of disease. Understanding their simple developmental origin can provide significant reassurance and demystify their presence.

• National Institutes of Health, Genetic and Rare Diseases Information Center (GARD). (2017). Supernumerary nipples. Retrieved from https://rarediseases.info.nih.gov/diseases/5425/supernumerary-nipples
• National Organization for Rare Disorders (NORD). (2022). Supernumerary Nipples. Retrieved from https://rarediseases.org/rare-diseases/supernumerary-nipples/
• Mayo Clinic. (2023). Extra nipples (supernumerary nipples). https://www.mayoclinic.org
• Genetics Home Reference. (2023). Polymastia and polythelia. https://ghr.nlm.nih.gov