What does skin cancer look like?
Not all growths on the skin are skin cancer. And not all skin cancers look alike. Pictured below are examples of basal cell and squamous cell carcinoma—together called nonmelanoma skin cancers. But keep in mind there's tremendous variability, even within each type of skin cancer. A nonmelanoma skin cancer can be smooth or crusty or even-colored or pigmented, and the borders may or may not be well defined. You should have a dermatologist look at anything that persists for three or more weeks (or seems to go away then comes back) or bleeds easily.
Melanoma, also pictured below, is different in that most arise from an existing mole. But as a melanoma grows, it causes changes that distinguish it from a mole. The warning signs, sometimes referred to as the ABCDs of melanoma, are: Asymmetry (one half doesn't match the other half); Border irregularity (the edges are ragged); Color variability (the pigmentation is uneven, with various colors present); and Diameter (larger than a pencil eraser, or about one-quarter inch across). Some experts have urged that a fifth letter be added: E, for evolving. The idea is that early melanomas often change in appearance, so be on the lookout for changes in size, shape, bleeding, color, and symptoms such as itching or soreness.