Ever heard of such a thing? Well, it happens. While developing in utero, a baby has a cellular hiccup (my term—you won't find it in a dictionary) and a third nipple is born.

The small but distinct nipple and areola will usually appear on the upper chest, but it can occasionally appear a bit lower down. A third nipple is so tiny at first and its appearance is so subtle, that it's usually not noticed right away after the baby is born. Most mothers think it's a birth mark unless the pediatrician points it out. It will remain flat and won't develop into a breast.

So does a third nipple increase breast cancer risk? No actual studies have been conducted, but at this point we don't think so. Nowhere in the scientific literature is any mention made of breast cancer ever growing within a third nipple.