Mongolian spot

Mongolian spots are produced by melanocyte leftovers that do not migrate into the epidermis; they remain deeper than usual in the lumbar-sacral region, resulting in blue coloration of the skin. Mongolian spots occur mainly on the buttocks and lower back, and occasionally on the abdomen, thighs, and arms. They occur in 90 percent of Blacks, 80 percent of Orientals and Native Americans, and 9 percent of Whites.