A Mongolian spot, also known as Mongolian blue spot,
congenital dermal melanocytosis, and dermal melanocytosis
is a benign, flat, congenital birthmark with wavy borders and irregular shape,
discovered on and named after Mongolians by Erwin Bälz.
It normally disappears three to five years after birth and almost always by puberty.
The most common color is blue, although they can be blue-gray, blue-black or even deep brown.