September 17, 2011

Nevi, commonly referred to as moles, beauty marks, or birthmarks, are one of the many types of benign tumors of the skin. Moles can be present at birth or develop during childhood or adulthood. A normal mole can be flat or raised and is generally an evenly colored brown, tan, or black spot on the skin. It can be round or oval. Moles are generally less than 1/4 in. or 6 mm in diameter. Once a mole has developed, it will usually stay the same size, shape, and color for many years.

Congenital moles or birthmarks are a less common kind of mole. Congenital moles are present at birth and are usually larger (>1.5 cm) than moles that develop after birth. They may be brown or black and sometimes pink. Smaller birthmarks are usually pigmented and often slightly raised. Giant congenital moles may be found anywhere on the skin and can cover large areas of the body. The risk of developing melanoma in these giant moles is high.

The number of moles increases with age, especially during childhood and adolescence. Boys tend to have more moles than girls do. Individuals with a family history of skin cancer tend to have more moles. Both children and adults who are sun sensitive are at increased risk of having or developing moles. Sun sensitivity can be measured as red or blond hair, light or fair skin color, a tendency to burn, a tendency to freckle, and a lack of tanning ability. Both benign moles and melanoma (cancer) occur more often in people with a lighter complexion.

Moles that are irregular in shape, size, or color may be referred to as atypical or dysplastic moles. These moles tend to be large. They form a continuum between the common mole and superficial spreading melanoma. Dysplastic moles may occur as multiple moles distributed over the body, a condition known as dysplastic nevus syndrome. People with multiple moles often have a family history of multiple moles and melanoma, and are at higher risk for developing melanoma themselves. Such people need to be closely monitored by a dermatologist. The association of increasing numbers of moles with melanoma suggests that moles are either markers of some exposure that leads to melanoma, or potential precursors of melanoma or both.

Sun exposure is the major risk factor leading to the development of skin melanoma and precursor lesions such as moles. Childhood sun exposure may promote the development of melanoma by increasing the number of moles that develop. Several studies have found more moles on sun-exposed areas of the body compared to sun-protected areas. After early sun exposure causes moles to develop, other risk factors for melanoma may cause the moles to progress to melanoma. Sunburns are related to both sun exposure and the skin’s sensitivity to the sun. Various studies have found an increased risk of moles with increasing number of sunburns, similar to the association seen between sunburns and melanoma.

The contribution of tanning bed use or sunless tanning products to the development of moles has not been well-studied at this time. Similar to sun exposure, ultraviolet light from tanning bed use during adolescence is likely to increase the number of moles. Any changes in a mole seen after tanning bed use should be shown to a dermatologist immediately.

Few moles develop into melanoma. Individuals with many moles have a greater chance that progression will occur. It is important to recognize changes in a mole in both children and adults. Photographs or full body charts of your moles can be used to monitor changes in shape, color, and size over time. The most important warning sign for melanoma is a spot on your skin that is changing in size, shape, or color over a period of 1 month to 1 or 2 years. The ABCD rule may help you remember the four signs of melanoma. If you find one of the following, consult a dermatologist: asymmetric—if half of the mole does not match the other half; B—irregular border—a mole forms irregular borders or becomes ragged, notched, or blurred; C— change in color—a mole changes in color or is not the same color all over; D—large diameter—a mole is larger than the width of a pencil eraser (more than 1/4 in. or 6 mm in diameter).

Seeking medical attention for suspicious moles is very important because melanoma can be a deadly disease with few or no symptoms or pain. However, melanoma is also easily curable if identified early and removed. Distinguishing between a mole and a melanoma may be difficult, even for dermatologists. The most dependable method to distinguish a normal mole from melanoma is to remove the mole and have it examined under a microscope to determine whether the lesion is cancerous.

SEE ALSO: Cancer, Melanoma, Skin care

Suggested Reading

  • Augustsson, A., Stierner, U., Rosdahl, I., & Suurkula, M. (1991). Melanocytic naevi in sun-exposed and protected skin in melanoma patients and controls. Acta Dermato-Venereologica, 71(6), 512-517.
  • Dennis, L. K., & White, E. (1994). Risk factors for the prevalence of nevi: A review. In R. P. Gallagher & J. M. Elwood (Eds.), Epidemiological aspects of cutaneous malignant melanoma. Boston: Kluwer.
  • Elder, D. E. (1989). Human melanocytic neoplasms and their relationship with sunlight. Journal of Investigative Dermatology, 92(Suppl. 5), 297S-303S.
  • Rigel, D. S., & Carucci, J. A. (2000). Malignant melanoma: Prevention, early detection, and treatment in the 21st century. CA: A Cancer Journal for Clinicians, 50(4), 215-236.


Category: M