Health A-Z

Medical Content Created by the Faculty of the Harvard Medical School


What Is It?

Melanoma is cancer of the cells ("melanocytes") that give skin its color. It develops when these cells change and reproduce aggressively. The number of cases of melanoma, the deadliest form of skin cancer, is increasing faster than any other cancer.

Doctors aren't sure why melanoma rates are soaring. It could be from spending too much time in the sun during outdoor activities. It could also be due to global changes, such as the depletion of the ozone, which absorbs many of the sun's harmful rays.

Your pattern of sun exposure appears to affect your risk of developing melanoma more than the total amount of sun exposure in your lifetime. Short bursts of intense sun seem most dangerous, especially if you get sunburned. Being out in the sun can cause changes (mutations) in skin cells' genes. Researchers have recently found several gene mutations shared by many melanoma tumor cells. It is likely that one or more of these mutations starts the cancer.

The most common type of melanoma spreads on the skin's surface. It is called superficial spreading melanoma. It may stay on the surface or grow down into deeper tissues. Other types of melanoma can start anywhere on or inside the body.

Your risk of developing melanoma is higher if you have:

  • Red or blond hair

  • Green or blue eyes

  • Fair skin

  • A history of being in the sun a lot, especially as a child

  • A mother, father, sister or brother with melanoma. If one of these relatives has melanoma, you are eight times more likely to develop it.

Features of freckles or moles that raise your risk of melanoma include:

  • A new mole appearing after age 30

  • A new mole at any age if it is in an area rarely exposed to the sun

  • A change in an existing mole

  • One or more atypical moles—moles that look like a fried egg or moles that are darker than others or have irregular borders or an irregular shape.

  • 20 or more moles larger than 2 millimeters across

  • 5 or more moles larger than 5 millimeters across (larger than a pencil eraser)

  • Freckles caused by being in the sun

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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