What is a third nipple and how many people have them?

Nipples are an often-controversial body part, even though they shouldn't be. Everyone has two of them, right? Well, except for people who have three.

Yes, third nipples exist, and they're more common than you might think. Also called accessory nipples or supernumerary nipples, these extra nubs exist in 1 to 5 percent of the population. The condition is considered a minor birth defect and is officially called polythelia. In some rare cases, a third nipple may be accompanied by extra breast tissue — a condition known as polymastia.

You might be positive that you don't have a third nipple, but you could be wrong. "A lot of people have them but never give them a second thought," Dr. Anne Taylor, a plastic surgeon, told Yahoo. "They think they're a mole." Third nipples don't necessarily appear in the chest area, either, but are typically found along the "embryonic milk lines" of the body which range from the area just above your armpit and extend all the way down past your chest and abdomen, ending at your upper inner thighs (around the groin area).

Where do third nipples come from? According to Taylor, many things "form and then regress" at the embryo stage of development. These third nipples are formed in the womb and, on some people, never fully regress. They're typically very small, making them even easier to overlook. They're also more likely to occur in men.

Third nipples don't present any danger (although third nipples accompanied by breast tissue should be monitored for breast disease), but some people might be sensitive about their appearance. The good news is that they can easily be removed by a dermatologist or a plastic surgeon, although some people choose to embrace their third nipples. Mark Wahlberg and Harry Styles both have third nipples (Styles actually has a fourth) and it clearly hasn't affected their success one bit.