The ABCDE rule is an effective way of recognizing skin cancer, Dr. Hale says. Asymmetry: Look at your moles and see if they have irregular shapes or two different looking halves. Border: Edges that seem blurred, rough or notched may be an indication of a problem. Color: Most moles are brown, black or pink. See your doctor if they change color at any point or spot. Diameter: “We’ve gotten much better at diagnosing very small melanomas, which is why the diameter factor is not as important anymore,” Dr. Hale says. Still, you should see a dermatologist if you have moles with a diameter of more than a quarter of an inch. Evolution: “This is the most important one,” Dr. Hale says. If you see any change at all in any of the moles you have, you should see a doctor right away.