Moles (nevi) are small, usually dark, skin growths that develop from pigment-producing cells in the skin (melanocytes).
Moles vary in size from small dots to more than 1 inch (about 2.5 centimeters) in diameter. Almost everyone has a few moles, and many people have large numbers of them. Moles may be flat or raised, smooth or rough (wartlike), and may have hairs growing from them. Although they are usually brown or dark brown, some moles are flesh-colored or yellow-brown. They may be red at first but often darken.
Moles commonly develop in childhood or adolescence, although in some people they continue to develop throughout life. Moles respond to changes in hormone levels in women and may first appear, enlarge, or darken during pregnancy. Once formed, moles remain for a lifetime and get less pigmented and more raised or fleshy with time. In fair-skinned people, moles occur more commonly on sun-exposed areas of the skin.
Moles usually are easily recognized by their typical appearance. They do not itch or hurt, and they are not a form of cancer. However, moles sometimes develop into or resemble melanoma, a cancerous growth of melanocytes (see Skin Cancers: Melanoma). In fact, many melanomas begin in moles, so a mole that looks suspicious should be removed and examined under a microscope.
The following changes in a mole are warnings of melanoma:
People with more than 10 or 20 moles have a somewhat increased risk of melanoma. They should self-monitor for changes in their moles and also have them examined periodically as part of their primary care. If a mole proves to be cancerous, additional surgery may be needed to remove the skin surrounding it.
Most moles, however, are harmless and do not require removal. Depending on their appearance and location, some moles may even be considered beauty marks. Normal moles that are unattractive or located where clothing can irritate them can be removed by a doctor using a scalpel and a local anesthetic.
Atypical Moles (Dysplastic Nevi):
Atypical moles tend to be multicolored and have irregular shapes and borders or increased size in comparison with normal moles. The tendency to grow atypical moles is hereditary. People with even a few atypical moles have a slightly increased risk of developing melanoma. This risk increases greatly if the person has close family members with melanoma.
People with atypical moles—particularly those with a family history of melanoma—must look for any changes that might indicate melanoma. They should have their skin checked at least yearly by a dermatologist to look for changes in the color or size of a mole. To help monitor such changes, dermatologists often use full-body color photographs. Atypical moles that change should be removed.
Sunlight accelerates the development of and changes in atypical moles. Even moderate sun exposure during childhood may be harmful and increase the risk of developing melanoma decades later. Therefore, people with atypical moles should avoid sun exposure. When in the sun, they should always use a sunscreen or sunblock with a high sun protection factor (SPF) rating to help shield against cancer-producing ultraviolet (UV) rays (see Sunlight and Skin Damage: Overview of Sunlight and Skin Damage).
Last full review/revision September 2008 by Daniel W. Collison, MD