Roughly one in every twenty people has a supernumerary nipple, commonly called a third nipple. Clinical surveys consistently place the prevalence somewhere between about 4% and 6% of the general population, though the true number may be higher because many people never realize what that small bump on their torso actually is. The condition is far more common than most people assume, and far less medically significant than old textbooks once warned.
Why the Prevalence Estimates Vary
If you search for a single definitive number, you will find a range instead. A prospective clinical study of 502 patients found that about 5.6% had a supernumerary nipple, typically small enough that the areola measured less than 30% of a normal areola’s diameter.1PubMed. Supernumerary nipples: prevalence, size, sex and side predilection — a prospective clinical study A separate study screening newborns and schoolchildren reported rates of about 4.3% in newborns and nearly 5.9% in schoolchildren.2PubMed. Supernumerary nipples and renal anomalies Some older references cite numbers as low as 1%, while certain population-specific screenings have reported figures above 6%.
The spread comes down to a few things. First, many supernumerary nipples are tiny. They can look like a mole, a birthmark, or a slightly raised patch of skin. Unless a clinician specifically examines for them, they go uncounted. Second, the definition matters: some studies count only nipples with clearly identifiable areolar tissue, while others include any remnant along the milk line that shows characteristic features under a microscope. Third, ethnicity and geography play a role. Some populations appear to have modestly higher rates than others, though no single ethnic group is dramatically overrepresented. The honest summary is that if you gathered a hundred random people, somewhere between four and six of them would likely have one.
Men and women both develop supernumerary nipples, though some clinical series have reported slightly higher rates in males. The difference is not dramatic enough to call it a strongly sex-linked trait, and many researchers consider the sex ratio roughly equal once you account for differences in how carefully subjects are screened.
Where They Form and Why
During early embryonic development, every human fetus develops a pair of ridges running from the armpit area down through the chest, past the abdomen, and into the groin. These ridges are called the milk lines, and they are the same structures that give rise to the two normal nipples everyone has. In most people, the tissue along the milk lines breaks down except at two points on the chest, leaving the standard pair. In people with supernumerary nipples, a small patch of mammary tissue elsewhere on the line fails to regress completely.
Supernumerary nipples develop along these embryonic milk lines on the chest and abdominopelvic regions.3PubMed Central. Implications of a Supernumerary Nipple Breast Cancer in a BReast CAncer Sequence Variation Carrier: A Case Report Histological studies confirm that this is the most common pathway: the remnant tissue sits over the front of the trunk, right along the route the milk lines took during fetal development.4PubMed. Supernumerary nipple. A histologic study This is why the most common location for a third nipple is below and slightly to the inside of a normal nipple, often on the left side (though right-sided and bilateral cases occur too).
The milk-line concept is not unique to humans. Across mammals, nipple number and placement are linked to the same embryonic ridges, with nipples positioned bilaterally along these lines. Some marsupials even have an odd number of nipples because they develop extras on the midline.5bioRxiv. The coevolution of mammae number and litter size In humans, the standard number settled at two because our species typically carries one or two offspring per pregnancy. A supernumerary nipple is essentially a leftover from a developmental blueprint that could have produced more.
Ectopic Nipples and Unusual Locations
Most supernumerary nipples sit squarely on the milk line, which means somewhere between the armpit and the groin on the front of the body. But a small number show up in truly unexpected places, including the back, the shoulder, the thigh, and even the sole of the foot. These are called ectopic supernumerary nipples, and they are genuinely rare. Dorsal presentations, meaning on the back, are considered exceptional.6SpringerLink. Dorsal midline ectopic mammary tissue as a cutaneous marker of spinal dysraphism: intradural lipoma and tethered cord in a child with literature review
Ectopic cases get more medical attention than the ordinary milk-line variety, partly because their unusual location makes them harder to identify and partly because some of them have been linked to underlying anatomical issues. In one documented case, ectopic mammary tissue on the back served as a surface marker for a spinal cord abnormality in a child. That kind of association is uncommon, but it illustrates why a bump in an odd location sometimes deserves a second look from a doctor, even if the bump itself is harmless.
When a “Third Nipple” Is Not a Third Nipple at All
Here is one of the more surprising findings from recent research: a large pathology study examining 161 lesions clinically diagnosed as supernumerary nipples found that about a third of them were something else entirely. Of the 161 lesions, 107 showed actual breast glandular tissue under the microscope, confirming them as genuine supernumerary nipples. But 54 lesions, initially diagnosed as accessory nipples, had to be reclassified as “clinical pseudo-polythelia.” These turned out to be moles in almost half the cases, with the rest including conditions like seborrheic keratosis and hemangiomas.7PubMed. Polythelia (Supernumerary Nipple): Clinicopathological Characterization of an Atavistic Lesion
This matters for two reasons. First, it suggests that the commonly quoted prevalence numbers could be overestimates if some clinical studies counted moles and benign skin lesions as nipples. Second, and more practically, it means that if you have a small bump on your chest or abdomen that you have always assumed was a third nipple, there is a real chance it is actually a mole or another benign skin feature. The only way to know for certain is histological examination after a biopsy or excision, which most people never bother with because the bump causes no symptoms either way.
Among the genuine supernumerary nipples in that study, the internal anatomy was diverse. About 80% of confirmed lesions contained ductal tissue, and roughly 20% contained lobular tissue. The majority also had nipple-type smooth muscle. In other words, the tissue is not just cosmetic pigmentation; it is structurally similar to normal breast tissue, just smaller and incomplete.
Does It Run in Families?
The short answer is that supernumerary nipples do appear to have a genetic component, though no single gene has been pinned down as the cause. Familial clustering has been documented, with one report describing six cases of supernumerary nipples across three generations of a single family, including one member who also had extra breast tissue (polymastia) in addition to extra nipples.8PubMed. Familial polythelia over three generations with polymastia in the youngest girl That pattern strongly suggests a heritable component, likely following an autosomal dominant inheritance pattern with variable expression, meaning you only need to inherit one copy of the relevant gene variant, but the trait does not always show up the same way in every carrier.
That said, most people with a supernumerary nipple do not have a dramatic family history of them. The trait can appear sporadically, without any known relatives who share it. This is typical of developmental variations that involve multiple genes interacting with each other and with environmental factors during fetal growth. If one of your parents has an extra nipple, your odds of having one are probably modestly higher than average, but it is far from guaranteed.
The Old Worry About Kidney Problems
For decades, a widely cited idea held that supernumerary nipples were a marker for kidney abnormalities. The theory, first popularized in the 1970s, proposed that because the kidneys and the mammary ridges develop around the same time during embryonic life, a disruption in one system might signal a disruption in the other. Pediatricians sometimes ordered kidney imaging for children found to have extra nipples based on this concern.
The evidence behind the link turned out to be weaker than initially claimed. One study that specifically evaluated 65 patients with supernumerary nipples found that about 11% had a significant kidney abnormality on imaging. However, some of those patients had other signs suggesting a urinary tract problem, and the researchers concluded that while an association probably exists, it is “significantly weaker than that originally proposed.”9PubMed. Does a supernumerary nipple/renal field defect exist? Older literature had also listed associations with cardiac conduction disturbances and congenital heart disease.10PubMed. Polythelia and associated conditions
Current thinking among pediatricians has shifted. Most do not recommend routine kidney ultrasound solely because a child has a supernumerary nipple, unless other clinical signs or a family history of urinary tract problems are present. The old practice of automatically ordering imaging for every baby with an extra nipple has largely been abandoned. If you have a third nipple and otherwise feel fine, this particular concern is not something you need to lose sleep over.
Supernumerary Nipples and Cancer Risk
Because many supernumerary nipples contain actual breast glandular tissue, a natural question is whether that tissue can develop cancer. The answer is yes, but the risk is very low. Case reports exist of breast cancer arising in supernumerary breast tissue, including one documented case in a patient who also carried a gene variant associated with hereditary breast cancer.3PubMed Central. Implications of a Supernumerary Nipple Breast Cancer in a BReast CAncer Sequence Variation Carrier: A Case Report But case reports describe individual events, not population-level risk. There is no large-scale evidence showing that people with supernumerary nipples face a meaningfully elevated cancer risk compared to the general population.
The practical concern is not that cancer in a third nipple is common. It is that if a change does occur in the tissue, such as a new lump, skin changes, or discharge from the extra nipple, it might be dismissed as irrelevant because people tend to assume third nipples are purely cosmetic remnants. Anyone who notices a change in the area should have it evaluated, the same way they would for any new lump anywhere on the body.
Body Image and Removal
For most people, a supernumerary nipple is a minor anatomical curiosity. Many never even realize they have one, or they notice it and forget about it. But for some, particularly during adolescence and young adulthood when body-image concerns are heightened, the extra nipple can be a source of self-consciousness.11International Journal of Surgery Case Reports. Isolated supernumerary nipple along embryonic milk line in an adult male patient successfully treated by surgical excision: a case report The effect is often worse when the nipple is large enough to be visible through clothing or when it sits in a location that draws attention.
Surgical removal is straightforward in most cases. It is typically done as a minor outpatient procedure under local anesthesia. The excised tissue is usually sent for histological examination, which serves the dual purpose of confirming what the lesion actually was and ruling out anything abnormal in the tissue. Some people pursue removal for cosmetic reasons, others because the nipple causes irritation from rubbing against clothing, and a small number do so on medical advice because of a palpable lump or other change in the tissue.
There is no medical necessity to remove a supernumerary nipple that is not causing symptoms. Many people live their entire lives with one and never give it a second thought. The decision is personal, and no guideline recommends prophylactic removal purely because the nipple exists.
Myths, History, and Pop Culture
Supernumerary nipples have carried a surprising range of cultural baggage over the centuries. In some historical contexts, extra nipples were considered a sign of heightened fertility or femininity. Anne Boleyn, the second wife of Henry VIII, was famously rumored to have had a third breast, though historians generally regard this as slander fabricated by her political enemies rather than a reliable anatomical description.12PubMed. Supernumerary breast tissue: historical perspectives and clinical features During the European witch trials, extra nipples were sometimes cited as evidence of witchcraft, allegedly serving as “witch’s teats” for suckling demonic familiars. The moles and skin tags that prosecutors pointed to were almost certainly ordinary skin lesions, but the association cemented the idea that extra nipples were somehow supernatural.
In modern pop culture, the third nipple has become more of a punchline than a stigma. Fictional characters with extra nipples appear in comedies, and several public figures have openly discussed having one. That shift toward casual acceptance tracks with what the medical literature actually says: for the overwhelming majority of people who have one, a supernumerary nipple is medically trivial and anatomically unremarkable.
How Supernumerary Nipples Are Classified
Not all supernumerary nipples are created equal. The most widely used classification system breaks them into several categories based on which tissue components are present:
- Category I (polymastia): a complete extra breast with nipple, areola, and underlying glandular tissue. This is the rarest form.
- Category II: a nipple and areola sitting above glandular tissue, but without the full breast mound.
- Category III: a nipple and areola only, with no glandular tissue beneath.
- Category V (polythelia): a nipple alone, without any surrounding areola or underlying breast tissue. This is among the most common presentations.
- Category VI: an areola alone, sometimes called “polythelia areolaris.”
In practice, most supernumerary nipples fall into the simpler categories. They are small patches of slightly pigmented skin, sometimes with a barely raised central nub, that blend in with the surrounding skin and attract little attention. The rarer categories involving substantial glandular tissue are more likely to be noticed and more likely to prompt medical evaluation, but they represent the minority of cases. A case report of a 13-year-old girl with bilateral supernumerary nipples illustrates a less common presentation: paired extra nipples on both sides of the body.13Europe PMC. Polythelia in a 13-year old girl
Can a Third Nipple Produce Milk?
This depends entirely on whether the supernumerary tissue contains functional glandular tissue. If it does, and that tissue responds to the hormonal changes of pregnancy, then yes, the extra nipple can produce milk. There are case reports of women who experienced lactation from a supernumerary nipple during breastfeeding. The milk is normal breast milk; the tissue is biologically the same, just located somewhere it is not expected.
Most supernumerary nipples do not contain enough glandular tissue to produce noticeable milk, and the majority of women who have one never experience anything from it during pregnancy. But it is not unheard of, and if it happens it is not dangerous. The tissue is simply doing what breast tissue does. For the same reason, supernumerary nipples in women can occasionally swell or become tender in sync with menstrual cycles, responding to the same hormonal fluctuations that affect normal breast tissue. In men, the extra tissue is generally too rudimentary to cause any noticeable hormonal response.