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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Epidermal nevus

Reviewed June 2011

What is epidermal nevus?

An epidermal nevus (plural: nevi) is an abnormal, noncancerous (benign) patch of skin caused by an overgrowth of skin cells. Epidermal nevi are typically seen at birth or develop in early childhood. They can be flat, tan patches of skin or raised, velvety patches. As the affected individual ages, the nevus can become thicker and darker and develop a wart-like (verrucous) appearance. Often, epidermal nevi follow a pattern on the skin known as the lines of Blaschko. The lines of Blaschko, which are invisible on skin, are thought to follow the paths along which cells migrate as the skin develops before birth.

There are several types of epidermal nevi that are defined in part by the type of skin cell involved. The epidermis is the outermost layer of skin and is composed primarily of a specific cell type called a keratinocyte. One group of epidermal nevi, called keratinocytic or nonorganoid epidermal nevi, includes nevi that involve only keratinocytes. Other types of epidermal nevi involve additional types of epidermal cells, such as the cells that make up the hair follicles or the sebaceous glands (glands in the skin that produce a substance that protects the skin and hair). These nevi comprise a group called organoid epidermal nevi.

Some affected individuals have only an epidermal nevus and no other abnormalities. However, sometimes people with an epidermal nevus also have problems in other body systems, such as the brain, eyes, or bones. In these cases, the affected individual has a condition called an epidermal nevus syndrome. There are several different epidermal nevus syndromes characterized by the type of epidermal nevus involved.

How common is epidermal nevus?

Epidermal nevi affect approximately 1 in 1,000 people.

What genes are related to epidermal nevus?

Mutations in the FGFR3 gene have been found in approximately 30 percent of people with a type of nevus in the keratinocytic epidermal nevi group. The gene mutations involved in most epidermal nevi are unknown.

Mutations associated with an epidermal nevus are present only in the cells of the nevus, not in the normal skin cells surrounding it. Because the mutation is found in some of the body's cells but not in others, people with an epidermal nevus are said to be mosaic for the mutation.

The FGFR3 gene provides instructions for the fibroblast growth factor receptor 3 (FGFR3) protein. This protein is involved in several important cellular processes, including regulation of growth and division of skin cells. The FGFR3 protein interacts with specific growth factors outside the cell to receive signals that control growth and development. When these growth factors attach to the FGFR3 protein, the protein is turned on (activated), which triggers a cascade of chemical reactions inside the cell that control growth and other cellular functions.

The most common FGFR3 gene mutation in epidermal nevi creates a protein that is turned on without attachment of a growth factor, which means that the FGFR3 protein is constantly active. Cells with a mutated FGFR3 gene grow and divide more than normal cells. In addition, these mutated cells do not undergo a form of self-destruction called apoptosis as readily as normal cells. These effects result in overgrowth of skin cells, leading to epidermal nevi.

Related Gene(s)

Changes in this gene are associated with epidermal nevus.

  • FGFR3

How do people inherit epidermal nevus?

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

Occasionally, the somatic mutation occurs in a person's reproductive cells (sperm or eggs) and is passed to the next generation. An inherited FGFR3 gene mutation is found in every cell in the body, which results in skeletal abnormalities rather than epidermal nevus.

Where can I find information about diagnosis or management of epidermal nevus?

These resources address the diagnosis or management of epidermal nevus and may include treatment providers.

  • Genetic Testing Registry: Epidermal nevus (

You might also find information on the diagnosis or management of epidermal nevus in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about epidermal nevus?

You may find the following resources about epidermal nevus helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for epidermal nevus?

  • epidermal naevus

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about epidermal nevus?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding epidermal nevus?

apoptosis ; benign ; cell ; epidermis ; fibroblast ; gene ; growth factor ; inherited ; keratinocyte ; mosaic ; mutation ; protein ; receptor ; reproductive cells ; somatic mutation ; sperm ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Brandling-Bennett HA, Morel KD. Epidermal nevi. Pediatr Clin North Am. 2010 Oct;57(5):1177-98. doi: 10.1016/j.pcl.2010.07.004. Review. (
  • Hafner C, Di Martino E, Pitt E, Stempfl T, Tomlinson D, Hartmann A, Landthaler M, Knowles M, Vogt T. FGFR3 mutation affects cell growth, apoptosis and attachment in keratinocytes. Exp Cell Res. 2010 Jul 15;316(12):2008-16. doi: 10.1016/j.yexcr.2010.04.021. Epub 2010 Apr 24. (
  • Hafner C, van Oers JM, Vogt T, Landthaler M, Stoehr R, Blaszyk H, Hofstaedter F, Zwarthoff EC, Hartmann A. Mosaicism of activating FGFR3 mutations in human skin causes epidermal nevi. J Clin Invest. 2006 Aug;116(8):2201-2207. (
  • Hafner C, Vogt T, Hartmann A. FGFR3 mutations in benign skin tumors. Cell Cycle. 2006 Dec;5(23):2723-8. Epub 2006 Dec 1. (
  • Hernández S, Toll A, Baselga E, Ribé A, Azua-Romeo J, Pujol RM, Real FX. Fibroblast growth factor receptor 3 mutations in epidermal nevi and associated low grade bladder tumors. J Invest Dermatol. 2007 Jul;127(7):1664-6. Epub 2007 Jan 25. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: June 2011
Published: February 1, 2016