The incidence of melanoma, the most serious and deadly type of skin cancer, is increasing. In the United States, the lifetime risk of developing melanoma is now about one in 70. It used to be less than one in 100.

“The best way to reduce your risk is to avoid sun exposure between 10 a.m. and 2 p.m, when the sun’s rays are strongest,” says Mark Pittelkow, M.D., Mayo Clinic dermatologist. “But, it’s a misconception to believe that melanoma occurs only with too much sun exposure, or that it occurs only on sun-exposed areas.”

In the June issue of Mayo Clinic Women’s HealthSource, Dr. Pittelkow shares insights on causes, prevention and warning signs of this potentially deadly cancer.

Causes: As with many types of cancers, melanoma results from a combination of environmental and genetic factors. That’s why melanoma can occur in areas not commonly exposed to sun, such as the genital area or on the scalp underneath hair.

Prevention: Staying out of the sun (or tanning beds) is best. A broad-spectrum sunscreen (which protects against both UVA and UVB radiation from the sun) with a sun protection factor (SPF) of at least 15 offers important protection when you are in the sun. But don’t rely on sunscreen alone to protect you and don’t abuse the benefits of sunscreen by staying out in the sun for long periods. Think of sunscreen as a supplement to other measures to protect you from UV radiation. Wear protective clothing, such as a wide-brimmed hat and tightly woven clothes to protect your arms and legs.

Warning signs: If you have a number of moles, try to do a full-body skin check every three to six months. If you don’t have moles and things haven’t changed, once a year is adequate.

Warning signs include moles that are: asymmetrically shaped; have a border that’s notched, scalloped, or otherwise irregular; nonuniform in color; larger than one-fourth inch across; or changing or growing.

Early treatment: If you find a small lesion, about one-eighth inch, that has one or more warning signs, see your primary care doctor or dermatologist. In many cases, surgery alone cures thinner lesions. The cure rates are typically very high - more than 95 percent five-year survival rates - for cancers that are less than 1 millimeter thick.