Excessive sun exposure, especially during childhood and adolescence, is the greatest preventable risk factor for melanoma and other skin cancers. Other risk factors:

Moles, or non-cancerous skin tumors. People with many moles or large moles have an increased risk for melanoma.

Fair skin: Fair skin, freckling and light hair all increase melanoma risk, though the cancer can develop in people of all races.

Family history: About 10 percent of people with melanoma have a close relative (parent, sibling or child) with the disease.

Immune suppression: People who have been treated with medications that suppress the immune system are at greater risk for melanoma.

Age: About half of melanomas occur in people over 50, but the disease is on the increase among younger people, too.

Xeroderma pigmentosum: A rare, inherited condition that leaves people less able to repair sun damage, and so increases melanoma risk.

Sources: The American Academy of Dermatology; The American Cancer Society