"A changing mole is one of the clearest signs of skin cancer. Spotting it early gives your doctor a chance to treat it before it has time to spread. But how will you ever know a mole is changing if you never look at your skin?Once a month, you should be checking your skin from top to bottom, front to back in a full-length mirror. 'You're looking for changes in the size, shape, and color of moles, or new moles,' Dover says. If you spot anything, or if you've got a personal or family history of skin cancer, let your dermatologist do a full exam as well, Stein says." *