The number of people in the world who develop melanoma is increasing each year. In the United States, the number has more than doubled in the past 20 years. Experts believe that much of the worldwide increase in melanoma is related to an increase in the amount of time people spend in the sun.

Ultraviolet (UV) radiation from the sun and from sunlamps and tanning booths damages the skin and can lead to melanoma and other types of skin cancer. (Two types of ultraviolet radiation -- UVA and UVB -- are explained in the "Dictionary ¹" section.) Everyone, especially those who have dysplastic nevi or other risk factors, should try to reduce the risk of developing melanoma by protecting the skin from UV radiation. The intensity of UV radiation from the sun is greatest in the summer, particularly during midday hours. A simple rule is to avoid the sun or protect your skin whenever your shadow is shorter than you are.

People who work or play in the sun should wear protective clothing, such as a hat and long sleeves. Also, lotion, cream, or gel that contains sunscreen can help protect the skin. Many doctors believe sunscreens may help prevent melanoma, especially those that reflect, absorb, and/or scatter both types of ultraviolet radiation. Sunscreens are rated in strength according to a sun protection factor (SPF). The higher the SPF, the more sunburn protection is provided. Sunscreens with an SPF value of 2 to 11 provide minimal protection against sunburns. Sunscreens with an SPF of 12 to 29 provide moderate protection. Those with an SPF of 30 or higher provide high protection against sunburn. Sunglasses that have UV-absorbing lenses should also be worn. The label should specify that the lenses block at least 99 percent of UVA and UVB radiation.

Glossary Terms

A scale for rating the level of sunburn protection in sunscreen products. The higher the SPF, the more sunburn protection it gives. Sunscreens with a value of 2 through 11 give minimal protection against sunburns. Sunscreens with a value of 12 through 29 give moderate protection. SPFs of 30 or higher give high protection against sunburn. Also called sun protection factor.

A scale for rating the level of sunburn protection in sunscreen products. The higher the sun protection factor, the more sunburn protection it gives. Sunscreens with a value of 2 through 11 give minimal protection against sunburns. Sunscreens with a value of 12 through 29 give moderate protection. Sun protection factors of 30 or higher give high protection against sunburn. Also called SPF.

A substance that helps protect the skin from the sun's harmful rays. Sunscreens reflect, absorb, and scatter both ultraviolet A and B radiation to provide protection against both types of radiation. Using lotions, creams, or gels that contain sunscreens can help protect the skin from premature aging and damage that may lead to skin cancer.

Invisible rays that are part of the energy that comes from the sun. Ultraviolet radiation also comes from sun lamps and tanning beds. It can damage the skin and cause melanoma and other types of skin cancer. Ultraviolet radiation that reaches the Earth's surface is made up of two types of rays, called UVA and UVB rays. UVB rays are more likely than UVA rays to cause sunburn, but UVA rays pass deeper into the skin. Scientists have long thought that UVB radiation can cause melanoma and other types of skin cancer. They now think that UVA radiation also may add to skin damage that can lead to skin cancer and cause premature aging. For this reason, skin specialists recommend that people use sunscreens that reflect, absorb, or scatter both kinds of ultraviolet radiation. Also called UV radiation.