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Why Do People Have Birthmarks

Genetics

While some birthmarks may appear in several generations in a family, for the most part, heredity does not play a factor in birthmark formation. Vascular birthmarks, including hemangiomas and stork bites, result because of an overabundance of blood vessels. Pigmented birthmarks, including café au lait spots and slate grey nevi, are caused by an overabundance of pigment cells, called melanocytes. An overabundance of blood vessels or pigment cells is usually random and not inherited.

Certain birthmarks may indicate underlying conditions. Neurofibromatosis is a condition which occurs in about one in every three-thousand births in the United States and is often signaled by the presence of six or more café au lait spots. Half of neurofibromatosis cases are inherited with the rest occurring because of a genetic mutation.

Port wine stains may occur because of Klippel-Trenaunay-Weber syndrome, a genetic mutation that is believed to occur sporadically. Sturge-Weber syndrome is often accompanied with a port wine stain on the forehead and upper eyelid on one side of the face. The causes of this syndrome are unknown.

Prevalence

More than one in ten babies are born with some kind of vascular birthmark, such as hemangiomas and port wine stains. Eighty-five percent of these birthmarks are in the neck and face area.

Strawberry hemangiomas occur in about ten percent of newborns. Hemangiomas occur about five times more often in females than in males.

Also called stork bites, salmon patch birthmarks are present on about half of all babies.

Venous malformations, also called port wine stains, occur in about three-tenths of a percent of all births.

Race

Slate gray nevi occur mainly in babies of African, Asian, and Latin descent and were previously referred to as "Mongolian blue spots." In a 1976 Stanford University study of 1,058 infants under 72 hours of age, these nevi were present in 95.5% of the babies of African-American decent, 81% of the Asian babies, 70% of the Latino babies, and only 9.6% of the caucasion babies.

Hemangiomas occur most often in babies of Caucasian descent.