Mongolian spot
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. In 1883 it was described and named after Mongolians by Erwin Bälz, a German anthropologist based in Japan. 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 deep brown.
Cause
The Mongolian spot is a congenital developmental condition -- that is, one existing from birth -- exclusively involving the skin. The blue colour is caused by melanocytes, melanin-containing cells, that are usually located in the surface of the skin (the epidermis), but are in the deeper region (the dermis) in the location of the spot. Usually, as multiple spots or one large patch, it covers one or more of the lumbosacral area (lower back), the buttocks, sides, and shoulders. It results from the entrapment of melanocytes in the lower half to two-thirds of the dermis during their migration from the neural crest to the epidermis during embryonic development.
