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Sunlight and Ultraviolet Exposure

Sunlight and Ultraviolet Exposure

The vast majority of skin cancers are due to unprotected ultraviolet radiation (UV) exposure. Most of this radiation comes from sunlight, but some may come from artificial sources, such as tanning booths. The amount of UV exposure depends on the strength of the light, the length of exposure, and whether the skin is protected.

What Damage Occurs with UV?

The short-term results of unprotected exposure to UV rays are sunburn and tanning. Long-term exposure causes prematurely aged skin, wrinkles, loss of elasticity, dark patches (lentigos, that are sometimes called "age spots" or "liver spots"), actinic keratoses. and actual skin cancers. Actinic keratoses are small (usually less than 1/4 inch) rough or scaly spots. Usually they develop on the face, ears, back of the hands, and arms of middle-aged or older people with fair skin, although they can arise on other sun-exposed areas of the skin. Although actinic keratoses are slow-growing and usually do not cause any symptoms, they sometimes turn into squamous cell cancer.

The American Cancer Society estimates more than 1 million new cases of highly curable basal and squamous cell cancers will be diagnosed this year. The most serious form of skin cancer is melanoma, which is diagnosed in more than 60,000 people each year and causes several thousand deaths. During the 1970s, the incidence rate of melanoma increased rapidly at about 6% per year. Since 1981, however, the rate of increase slowed to about 3% per year.

Besides skin cancer, the sun's UV radiation also increases the risk of cataracts and certain other eye problems, and can suppress the immune system. And although dark-skinned people are generally less likely to get skin cancer than light-skinned people, they are susceptible to cataracts and immune suppression.

Are Any UV Rays Safe?

Two main types of UV radiation reach the earth, UVA and UVB. UVB radiation is well known to cause damage to the DNA of skin cells. Skin cancers develop when this damage affects the DNA of genes that control growth and division of skin cells. Recent research has found that UVA also contributes to skin cancer formation. Scientists now believe that both UVA and UVB rays contribute to skin damage, including skin cancer. There are no safe UV rays.

What Is the UV Index?

To increase awareness of the damaging potential of UV radiation, the Environmental Protection Agency and the National Weather Service developed the UV Index. The UV index number, ranging from 0 to 10+, indicates the amount of UV radiation reaching the earth's surface during an hour around noon. It is forecast daily for 58 cities, based on locally predicted conditions. The higher the number, the greater the exposure to UV radiation. The UV Index is valid only for about a 30-mile radius from the city, and, as with any forecast, local variability in cloud cover and other factors may change actual levels experienced, but it serves as a reminder to take precautions against UV exposure.

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