Most people have moles, and most moles are unimportant. However, atypical moles, which doctors call dysplastic nevi, are significant because some of them may be melanomas or may become melanomas. Distinguishing harmless atypical moles from melanomas can be difficult; in most cases, patients can't do this themselves. However, patients can play an important role in the early detection of melanomas by becoming familiar with what normal, typical moles look like and bringing moles that don't look normal to their doctors' attention.
Normal, typical moles usually have the following characteristics:
They have a round or oval shape and are symmetrical (one half looks like the other).
They have a regular, sharp border.
Their color is tan, brown, or the same color as the rest of the skin.
Their size is small (usually no bigger than a pencil eraser).
They are located primarily on areas of the body that are frequently exposed to the sun.
They first appear sometime between early childhood and age 40.
Their appearance is uniform, that is, the various moles on the individual's body tend to resemble one another.
Atypical moles may differ from typical moles in any or all of these characteristics. To make it easy to remember what atypical moles may look like, experts have devised an ABCD mnemonic, where A stands for "Asymmetry," B for "Border Irregularity," C for "Color Variation," and D for "Diameter" (larger than a pencil eraser, which is about 6 mm in diameter). Moles with any of these characteristics should be considered atypical and should be examined by a doctor, as should any mole that itches or bleeds or has changed in appearance.
Another group of moles that should be examined by a doctor are those that are present at birth (called congenital nevi). These moles are more likely than typical moles to develop into melanomas.
Most moles are not harmful and need no treatment unless they are causing irritation by rubbing against clothing or the patient wants them removed for cosmetic reasons. Even atypical moles are often harmless, although a doctor may need to perform a biopsy (a procedure in which a sample of tissue is removed and then examined under a microscope) to be sure that they are not cancerous. Biopsies or removal of moles are simple procedures that can usually be performed in a dermatologist's office.