You are higher risk if you have a personal or family history of skin cancers especially melanomas, if you have very fair skin which burns or freckles easily, if you have over 20 moles on your body, if you've had a lot of sun exposure or have a history of blistering sunburns, and if you have used tanning beds on a regular basis.

See Dr. Irwin's in depth article on Moles, Lumps, and Bumps.