Young Blonde Girl With The Forehead Birthmark

The Mongolian spot is a congenital developmental condition exclusively involving the skin. The blue colour is caused by melanocytes, melanin-containing cells, that are deep under the skin. Usually, as multiple spots or one large patch, it covers one or more of the lumbosacral area (lower back), the buttocks, flanks, and shoulders. It results from the entrapment of melanocytes in the dermis during their migration from the neural crest to the epidermis during embryonic development.
Among those who are not aware of the background of the Mongolian spots, it may sometimes be mistaken for a bruise indicative of child abuse.