<unk>  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. Male and female infants are equally predisposed to slate grey nevus. People who are not aware of the background of the slate grey nevus may mistake them for bruises, possibly resulting in mistaken concerns about abuse. Anthropological description The French anthropologist Robert Gessain interested himself in what he called the tache pigmentaire congenitale or coloured birthmark, publishing multiple papers in the Journal de la Société des Américanistes, an academic journal covering the cultural anthropology of the Americas. Gessain spent time with the Huehuetla Tepehua people in Hidalgo, Mexico, and wrote in 1947 about the spot's "location, shape, colour, histology, chemistry, genetic transmission, and racial distribution". He had previously spent several winters in Greenland, and wrote an overview in 1953 of what was known about the spot. He hypothesised that the age at which it faded in various populations might prove to be a distinguishing characteristic of those groups. Gessain claimed that the spot was first observed amongst the Inuit. Hans Egede Saabye, a Danish priest and botanist, spent 1770–1778 in Greenland. His diaries, published in 1816 and translated into several European languages, contained much ethnographic information. He described the spot on newborns, saying he had seen it often when the infants were presented naked for baptism. A second Danish observer was doctor and zoologist Daniel Frederik Eschricht, mainly based in Copenhagen. In 1849 he wrote of the "mixed" babies he had delivered at the lying-in hospital. He also says that "the observation made for the first time by Saabye about Inuit children has been completely confirmed by Captain Holbøll", who sent him a fetus pickled in alcohol. Gessain goes on to state that it was only in 1883 that an anthropologist mentions the spot. It was Erwin Bälz, a German working in Tokyo, who described a dark blue mark on Japanese infants. He presented his findings in 1901 in Berlin, and from that point on, Bälz's name was associated with certain skin cells containing pigment. Captain Gustav Frederik Holm wrote in 1887 that his Greenlandic interpreter Johannes Hansen (known as Hanserak) attested to the existence of the birthmark over the kidney region of newborns, which grows larger as they grow older. That year, the Danish anthropologist Soren Hansen drew the connection between the observations of Bälz in Japan and Saabye in Greenland. "This cannot be a coincidence. It is not the first time that the resemblance between the Japanese and the Eskimo has been pointed out." Fridtjof Nansen, the Norwegian polar explorer, said that the spot was widespread in the mixed Danish-Inuit population of West Greenland. Soren Hansen confirmed this. A missionary in Bethel, Alaska, a traditional gathering place of Yup'ik people, reported that the spots were common on children. Rudolf Trebitsch, an Austrian linguist and ethnologist, spent the summer of 1906 on the West Coast of Greenland, and listed all the examples he came across. Gessain went to north Labrador in 1926, looking for children with these spots. In 1953 Dr Saxtorph, medical advisor to the Greenland department (part of the Danish government), wrote that the Greenlanders do not like outsiders to see or discuss these birthmarks; "they doubtless feel as a reminiscence of the time when they lived on a low cultural level". The presence or absence of the slate grey nevus was used by racial theorists such as Joseph Deniker (1852-1918), the French anthropologist. The Journal of Cutaneous Diseases Including Syphilis, Volume 23 contained several accounts of the slate grey nevus on children in the Americas: In Central America, according to these authorities, the spot is called Uits, "pan," and it is an insult to speak of it. It disappears in the tenth month. It is bluish-reddish (in these Native people), and is remarkable by its small size. The mulberry colored spot is very well known in Afro-Brazilians. In Brazil, among individuals of mixed Indigenous American and West African descent (pardo) it is called "genipapo", from its resemblance in color (bluish-gray) to an indigenous fruit of Brazil, named genipapo (a Native word adopted into Portuguese).
Mongolian spot
Fuchs spot
Forchheimer spots
Bier spots
Fordyce spots
Elschnig spots
Koplik's spots
Bitot's spots