Melanoma is usually visible as a single dark skin spot. It may appear anywhere on the body, but it most commonly develops on the back, chest, and legs. Most of the time, melanoma develops on normal-looking skin, but it can grow out of an existing mole.
Watch a mole for the A, B, C, D and Es of melanoma:
Asymmetry (one side doesn't match the other)
Colors or shades of skin that are different within the same mole
Diameter larger than 6 millimeters (larger than a pencil eraser)
Evolving (a newly developing mole)
A mole that bleeds, feels numb, or has a crusty surface may also hint at melanoma.