No one knows the exact causes of melanoma. Doctors can seldom explain why one person gets melanoma and another does not. However, research has shown that people with certain risk factors are more likely than others to develop melanoma. Anything that increases the chance of developing a disease is called a risk factor.

Personal history of melanoma or skin cancer: People who have been treated for melanoma have a high risk of a second, separate melanoma. Some people develop more than two melanomas. People who have had one or more of the common skin cancers (basal cell carcinoma or squamous cell carcinoma) are also at increased risk of melanoma. These individuals should be in screening and surveillance programs and this risk assessment tool is not appropriate for them.

Family history of melanoma: Melanoma sometimes runs in families. Having close relatives who have had this disease is a risk factor. About 10 percent of all patients with melanoma have another family member with this disease; only about 1% of individuals with melanoma have more than one family member with melanoma. When melanoma runs in a family, all close family members of individuals with melanoma should be checked regularly by a doctor.

Many ordinary moles: Having many moles, particularly larger moles, increases the risk of developing melanoma.

Dysplastic nevi: Dysplastic nevi are larger, flat, irregular moles that are more likely than ordinary moles to become cancerous. Dysplastic nevi are relatively common, and many people have a few of these abnormal moles. The risk of melanoma is greatest for people who have a large number of dysplastic nevi. The risk is especially high for people with a family history of both dysplastic nevi and melanoma.

Fair skin or freckles: Melanoma occurs more frequently in people who have fair skin that burns or freckles than in people with dark skin, probably because light skin is more easily damaged by the sun. People who have freckles have had enough sun to damage their skin.

Severe, blistering sunburns: People who have had at least one severe, blistering sunburn are at increased risk of melanoma. Doctors particularly advise that parents protect children's skin from the sun. Such protection may reduce the risk of melanoma later in life.

Ultraviolet (UV) radiation: Melanoma is more common in people who live in areas that get large amounts of UV radiation from the sun. In the United States, for example, melanoma is more common in Texas than in Minnesota, where the sun is not as strong. UV radiation from the sun causes premature aging of the skin and skin damage that can lead to melanoma. Artificial sources of UV radiation, such as sunlamps and tanning booths, can also cause skin damage and increase the risk of melanoma. Doctors encourage people to limit their exposure to natural UV radiation and to avoid artificial sources.:

Weakened immune system: People whose immune system is weakened by certain cancers or other immune disorders, or by drugs given after organ transplantation, are at increased risk of developing melanoma. Although these conditions are not common, it would be advisable for such individuals to be in screening and surveillance programs.

People who are concerned about developing melanoma should talk with their doctor about the disease, the symptoms to watch for, and an appropriate schedule for checkups. The doctor's advice will be based on the individual's personal and family history, medical history, and other risk factors.

Doctors recommend that everyone take steps to help prevent and reduce the risk of melanoma and non-melanoma skin cancers caused by UV radiation:

• Avoid exposure to the midday sun (from 10 a.m. to 4 p.m.) whenever possible. When your shadow is shorter than you are, remember to protect yourself from the sun.
• Avoid exposure to artificial sources of UV radiation, such as sunlamps and tanning booths.
• If you must be outside, wear long sleeves, long pants, and a hat with a wide brim.
• Protect yourself from UV radiation that can penetrate light clothing, windshields, and windows.
• Protect yourself from UV radiation reflected by sand, water, snow, and ice.
• Protect yourself when you are at higher elevations, such as in the mountains.
• Help protect your skin by using a lotion, cream, or gel that contains sunscreen. Use sunscreens that reflect, absorb, and/or scatter both types of ultraviolet radiation. These sunscreen products will be labeled with "broad-spectrum coverage." Use a sunscreen with a Solar Protection Factor (SPF) of 15 or greater for more protection.
• Wear sunglasses that have UV-absorbing lenses. The label should specify that the lenses block at least 99 percent of UVA and UVB radiation. Sunglasses can protect both the eyes and the skin around the eyes.

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