Excerpted from MORE Magazine.

How to Spot It

Follow the ABCD rule for detecting skin cancer, which points to four signs that a skin lesion may be malignant:

A: It is asymmetrical. Draw an imaginary line through the middle of the mole, either vertically or horizontally. Are the two halves nearly the same size and shape? If not, get it checked by your dermatologist.

B: It has an irregular border. The edge or border of a melanoma is usually irregular. The border can be scalloped, ragged, notched, blurred, or poorly defined.

C: Its color is mottled or changing. Benign moles can be any color, but each mole will be only one color. Melanomas usually vary in shades within the same mole -- from tan to brown to black or even blue.

D: It has a diameter larger than the size of a pencil eraser. Be on the lookout for moles that are different from the others, one that changes, grows, itches, or bleeds. One of the most important warning signs is actually a new or changing lesion, says Martin A. Weinstock, MD, chair of the American Cancer Society's skin-cancer advisory group. Some experts even advocate adding an E, for evolving, to the ABCD rule.

If your mole "passes" any or all of these ABCDs, see a dermatologist, pronto. Don't delay, because once a melanoma has grown to the size of a dime it has a 50 percent chance of having spread elsewhere, says Darrell Rigel, MD, clinical professor of dermatology at New York University.

Don't let your doctor brush off a suspicious spot. If in doubt, have it taken out and insist on a biopsy, advises Kaufman. "Melanoma often arises from other moles, so removing them can be a preventative measure."

If you have more than 50 moles on your body, consider having a dermatologist make a detailed "mole map." These medical photos are used to detect whether there are changes to a mole during subsequent checkups.