Sunscreen is a substance worn to protect the skin from the damaging effects of sunlight, including sunburn and skin cancer. Sunscreen protects by absorbing or reflecting the invisible ultraviolet (UV) rays in sunlight (see Ultraviolet rays ). Scientists separate these rays into three categories, known as UVA, UVB, and UVC. Earth’s upper atmosphere absorbs most of the sun’s ultraviolet radiation. But some UVA and UVB rays penetrate and can cause sunburn. Overexposure to such rays can lead to skin cancer. Sunscreens are available as gels, lotions, sprays, and lip balm. Some cosmetics and moisturizers also contain sun-protective ingredients. However, many of these products provide little or no UVA protection.
Commercial sunscreens are available in various strengths. The strength is indicated by a number called a sun protection factor or SPF. An SPF of 2 means that, once applied, twice the usual time passes before the skin becomes sunburned. To be effective, sunscreen should have an SPF of 15 or higher. A sunscreen is labeled as broad-spectrum if it protects against both UVA and UVB rays. Broad-spectrum sunscreens help protect against both sunburn and skin cancer when used regularly.
Health professionals recommend that people protect exposed skin with a sunscreen of SPF 30 or greater. Exposed skin is any skin that is not protected from the sun by clothing. A person of fair complexion may need a higher SPF. A higher SPF is also recommended if the person will be outdoors for a long time or will have intense sun exposure, as happens in skiing or at the beach.
Sunscreen should be applied to all exposed skin 15 to 30 minutes before sun exposure. It is best to use two applications of sunscreen. One layer should be applied and let dry before applying the second. About 1 fluid ounce (30 milliliters) of sunscreen should be used to cover the arms, legs, neck, and face. More is needed to cover the chest and back. Using less sunscreen may reduce its ability to protect the skin, effectively lowering the SPF rating. Sunscreen should be reapplied every two to three hours.
See also Sunburn .
