Having four nipples means you have two extra (supernumerary) nipples, a condition called polythelia. It’s more common than most people realize. Studies estimate that about 1 in 18 people have at least one extra nipple, and having two extras, while less common, follows the same biology. The reason comes down to something that happened before you were born, during the first weeks of embryonic development.
How Extra Nipples Form Before Birth
Around week four of embryonic development, two ridges of tissue called “milk lines” form along the front of the body. Each line runs from the armpit area down through the chest, along the abdomen, and into the groin. In most mammals, multiple nipples develop along these lines (think of a dog or cat). In humans, only one nipple on each side is supposed to remain. The rest of the tissue along those ridges normally dissolves before birth.
When that tissue doesn’t fully regress, the leftover cells can develop into extra nipples. This is why most supernumerary nipples appear somewhere along that armpit-to-groin path, typically below the regular nipples on the chest or upper abdomen. In rare cases, they can show up in unexpected spots like the back, thigh, or neck.
Animal research suggests that a specific cell signaling pathway involved in breast tissue development may be responsible when it’s disrupted or overactive. The trait also runs in families. It most commonly follows an autosomal dominant inheritance pattern with incomplete penetrance, meaning a parent can carry and pass on the gene without necessarily having extra nipples themselves. If someone in your family has the trait, your chances of having it go up significantly.
What Extra Nipples Look Like
Extra nipples rarely look like your regular ones. Most are much smaller and are frequently mistaken for moles, birthmarks, or small skin-colored bumps. Some appear as a tiny raised pink or brown spot. Others look like a small dimple or indentation. In one study of extra nipples examined under magnification, many appeared clinically similar to dermatofibromas (firm skin bumps) or common moles. A key distinguishing feature is a small central cleft or slit visible on close examination, which moles don’t have.
There’s actually a classification system with eight different types, ranging from a complete extra breast with nipple, areola, and underlying glandular tissue all the way down to just a patch of hair. Most supernumerary nipples fall into the simpler categories: a nipple without an areola, an areola without a nipple, or a nipple and areola sitting over a pad of fat rather than breast tissue. If yours look like small flat spots or tiny bumps, they likely don’t have any glandular tissue underneath.
Who Gets Them
A prospective clinical study of 502 patients found supernumerary nipples in 5.6% of the group. Men are more likely to have them than women, with one study finding a male-to-female ratio of roughly 2.5 to 1. They also appear more often on the left side of the body than the right, though researchers aren’t sure why. Having two extras (giving you four total) simply means the milk line tissue persisted in two spots instead of one.
Hormonal Changes Can Affect Them
If your extra nipples contain any glandular tissue underneath, they can respond to the same hormonal shifts as regular breast tissue. This means they may enlarge during puberty, swell or become tender before a menstrual period, and in some cases even produce milk during pregnancy or breastfeeding. For the majority of people whose extra nipples are just surface tissue without glands, none of this applies. They simply sit there doing nothing.
The Kidney Connection
You may come across older medical literature linking extra nipples to kidney or urinary tract abnormalities. The evidence on this is mixed. Studies of otherwise healthy infants found no increase in kidney problems among those with supernumerary nipples. However, studies looking at children who already had other developmental differences did find higher rates of kidney anomalies, ranging from 8% to 23% in those groups. The current understanding is that isolated extra nipples in an otherwise healthy person aren’t a reliable marker for kidney issues. If you have no other symptoms or known conditions, the extra nipples alone aren’t a cause for concern.
Removal Options
Extra nipples don’t need to be removed for medical reasons in most cases. They carry the same low risk of tissue changes as normal breast tissue, proportional to how much glandular tissue (if any) is present. Most people who choose removal do so for cosmetic reasons. The procedure is straightforward, typically involving a simple surgical excision under local anesthesia, similar to having a mole removed. If an extra nipple causes discomfort from friction, repeated irritation, or cyclical tenderness, that’s another practical reason some people opt for removal.