An epidermal nevus (plural: nevi) is an abnormal, noncancerous (benign) patch of skin caused by an overgrowth of cells in the outermost layer of skin (epidermis). Epidermal nevi are typically seen at birth or develop in early childhood. Affected individuals have one or more nevi that vary in size.

Several genes have been associated with different types of epidermal nevus. Mutations in the FGFR3 gene and PIK3CA gene account for about forty percent of keratinocytic epidermal nevi. Mutations in the HRAS gene are found in a majority of people with a nevus sebaceous and are also associated with keratinocytic epidermal nevi. Genes related to HRAS (called KRAS and NRAS) are less commonly involved in nevi sebaceous or keratinocytic epidermal nevi. Other genes, some of which have not been identified, are also involved in epidermal nevi.

Epidermal nevi are estimated to occur in 1 to 3 in 1,000 people.

This condition is generally not inherited but arises from mutations in the body's cells that occur after conception. This type of alteration is called a somatic mutation.

Published Date: August 01, 2016Published By: National Institutes of Health