A mole (also called a “nevus”) is a small area of skin cells that have different pigmentation than the surrounding skin. They’re also called “beauty marks”. The darker color, brown or black, is caused by in increase in melanin in that area of the skin: darker skinned people have more melanocytes producing more melanin than lighter skinned people. Moles are simply small areas of increased melanin productivity.
Most people have some nevi. When you have them from birth, they’re called “congenital nevi”. We often grow more of them as we age. Some may disappear, too.

Large nevi (e.g., larger than a fist) are more likely to become skin cancers than small ones. Any changes in a nevus (mole) should be examined by a dermatologist; be aware of any changes in size, color, shape or texture. Also, if the nevus starts to itch or ulcerate or bleed, it might be an indication that a skin cancer has formed.

Also important to notice are Atypical (Dysplastic) Nevi. These are usually larger than other nevi, with uneven borders resulting in an unusual shape, or with varying shades of color. Some just refer to them as “funny looking” moles. They may resemble malignant melanoma, but are harmless.

Everyone should be aware of the ABCDE’s that make moles more likely to be skin cancers:

A) Asymmetry: one half of the mole does not look like the other half.
B) Border: the border is not regular, or it seems to flow into the surrounding skin.
C) Color: there are differences in color throughout the nevus.
D) Diameter: the mole is larger than ¼ inch from one side to the other.
E) Evolving: there is significant change in size, shape, or shade of color.

If you have more than 50 moles, you are more likely to have a skin cancer than otherwise.  Even moles hidden under your clothes can be cancerous; ask to have them examined.