|Classification and external resources|
Mongolian spot visible on six-month-old Taiwanese baby girl
|ICD-10||D22.5 (ILDS D22.505)|
|ICD-9||757.33 (CDC/BPA 757.386)|
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 is also extremely prevalent among East Asians, South-East Asians, Polynesians, Native Americans, East Africans, and Turkish people. 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.
The Mongolian spot is a congenital developmental condition exclusively involving the skin. The blue colour is caused by melanocytes, melanin-containing cells, that are usually located in the epidermis but are in the deeper region of the skin known as 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.
The condition is unrelated to gender; male and female infants are equally predisposed to Mongolian spot.
Rough estimates are that the Mongolian spots are most prevalent among infants of East Asian groups, American Indian 80-85%, and black infants. Infants may be born with one or more Mongolian spots ranging from small area on the buttocks to a larger area on the back. They also occur in about 90-95% and about 80-85% of East African and Native American infants, respectively. Approximately 90% of Polynesians and Micronesians are born with Mongolian spots, as are about 46% of Latin American children. These spots also appear on 5-10% of babies of full Caucasian descent; Coria del Río in Spain has a high incidence due to the presence of descendants of the first Japanese official envoy to Spain in the early 17th century.
Cultural references 
The Mongolian spot is referred to in the Japanese idiom shiri ga aoi (尻が青い), meaning "to have a blue butt,"  which is a reference to immaturity or inexperience. In Mexico, it is referred to as "la patada de Cuauhtémoc", meaning "Cuauhtémoc's kick". In Korea, it is thought that the Mongolian spot is the bruise formed when Samshin halmi(삼신할미), a Shaman spirit to whom people pray around child birth, has beaten in order for a baby to go out from his or her mother.
In the comedy manga series Joshiraku written by Kōji Kumeta, as well as in its anime adaptation, the character Marii Buratei is known to have a mongolian spot. In one sketch, a westerner notices the spot and mistakes it for child abuse, blaming "barbarian Japanese" and taking Marii to "safety" abroad, against her wishes.
See also 
- Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. p. 1720. ISBN 1-4160-2999-0.
- Die koerperlichen Eigenschaften der Japaner.(1885) Baelz.E. Mittheil.d.deusch Gesell.f.Natur-u-Voelkerheilkunde Ostasiens. Bd.4.H.32
- Circumscribed dermal melanosis (Mongolian spot)(1981) Kikuchi I, Inoue S. in "Biology and Diseases of Dermal Pigmentation", University of Tokyo Press , p83
- "Frequency and characteristics of mongolian spots among Turkish children in Aegean region". July, 2006.
- About Mongolian Spot
- Mongolian blue spots - Health care guide discussing the Mongolian blue spot.
- Mongolian Spot DrGreen.com
- Mongolian Spot - English information of Mongolian spot, written by Hironao NUMABE, M.D., Tokyo Medical University.
- Empson, Rebecca M. (2010). Harnessing fortune : personhood, memory and place in northeast Mongolia. Oxford: Oxford University Press. ISBN 9780197264737.
- Epidemiology of Mongolian spot on MedScape
- 尻 (Japanese)
- "The butt is blue": the untold story, Language Log, October 15, 2008 @ 3:14 pm; comment of October 16, 2008 @ 11:39 am