If you draw a line through the middle of a healthy mole, the two sides will match, meaning it is symmetrical. If you draw a line through a dangerous mole, the two halves will not match, meaning it is asymmetrical, a warning sign for melanoma.

A benign mole has smooth, even borders, unlike melanomas. The borders of an early melanoma tend to be uneven. The edges may be scalloped or notched.

Most benign moles are all one color — often a single shade of brown. Having a variety of colors is another warning signal. A number of different shades of brown, tan or black could appear. A melanoma may also become red, white or blue.

Benign moles usually have a smaller diameter than malignant ones. Melanomas usually are larger in diameter than the eraser on your pencil tip (¼ inch or 6mm), but they may sometimes be smaller when first detected.

Common, benign moles look the same over time. Be on the alert when a mole starts to evolve or change in any way. When a mole is evolving, see a doctor. Any change — in size, shape, color, elevation, or another trait, or any new symptom such as bleeding, itching or crusting — points to danger.