From Heather Brannon, MD,
Your Guide to Skin & Beauty.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

Moles are so common that everyone has them. Few people are born with moles, only 1 percent of newborns have them. The appearance of new moles peaks in puberty and slows after that.

The Origin of Moles

Moles are benign tumors that come from melanocytes. Melanocytes are cells in the skin that make the pigment, melanin. We don't really understand why some melanocytes are altered and develop into moles, although it seems to be linked to genetics and sun exposure.

Appearance of Moles

Not all moles look alike. Normal moles can be different colors -- flesh, brown, black, red, and even blue. They can be flat or raised, round, oval, or irregularly shaped. They can have an even distribution of color or be mottled. Typical moles have the following characteristics:

• Round
• Brown
• Raised
• Symmetrical
• Small
• Well-demarcated borders

Several factors may increase the size and pigmentation of moles:

• Puberty
• Pregnancy
• Sun exposure

Abnormal Moles

The cells of some moles can change into skin cancer, especially melanoma. These abnormal moles are called dysplastic nevi. Dysplastic nevi have a higher chance of developing into melanoma. It is important to learn how to do a skin self-examination to look for concerning changes in moles.

How to do a Skin Self-Examination

You should check your skin frequently to learn to recognize the usual appearance of your moles. Learn more about how to do a thorough skin self-examination here.

_Sources:

Barnhill, Raymond and Keith Llewellyn. "Benign Melanocytic Neoplasms". Dermatology. Ed. Jean L Bolognia, MD, et al. London: Mosby, 2003. 1768-70.

Habif, Thomas. "Nevi and Malignant Melanoma". Clinical Dermatology, 3rd ed. St. Louis: Mosby, 1996. 688-692.

"How to Perform a Self-Examination." American Academy of Dermatology. 2006. American Academy of Dermatology. 4 May 2007.