ABCD's of Moles and Skin Cancers
Asymmetry. If you could fold the lesion in two, the two halves would not match.
Border. Melanomas often have uneven or blurred borders.
Color. Melanoma typically is not one solid color; rather it contains mixed shads of tan, brown, and black. It can also show traces of red, blue or white.
Diameter. While melanomas are usually greater than 6 millimeters (about the size of a pencil eraser) when diagnosed, they can be smaller. If you notice a mole different from others, or which changes, itches, or bleeds even if it is smaller than 6 millimeters, you should see a dermatologist.