Ah, the mysterious third nipple. Why do some people have one, and how do they form? At the BBC, Jason Goldman reports that while some have considered the "supernumerary nipple" a fault of the evolutionary process, similar to wisdom teeth or the tailbone, recent research shows that extra-nipple formation may be far more involved. Here are key takeaways:
- Researchers are finding a correlation between gender, ethnicity, geographic region, and nipples. For instance, one study found 0.6% of white American infants have a third nipple, while their black American counterparts clock in at 1.63%; Israeli infants had an even higher rate of 2.5%.
- The supernumerary nipple is very unusual: Only an estimated 200,000 people are born in the US with what the National Institute of Health calls a "rare disease."
- Humans can and have had up to six additional nipples, though more than three is considered exceedingly rare.
- The nipples (both normal and supernumerary) form during the fourth week of embryo fertilization. Two strips of tissue across the chest (called "mammary ridges") regress in-utero, creating two nipples, but sometimes they don't regress completely, leaving an extra nipple.
- Some supernumerary nipples can contain breast tissue, and undergo the same hormonal changes as normal nipples.
- Though rare, supernumerary nipples exist in places other than the chest. One such "ectopic supernumerary nipple" was reportedly found on a French woman's thigh in 1827. It produced milk and "her infant ... took it willingly," writes Norman Grossl in the Southern Medical Journal.
Click for Goldman's full story
. (Read more human body