The Minnesota Poison Control System warns that 20 percent of Americans will develop skin cancer. Sun exposure contributes to this disease, but using an SPF15 or higher sun block regularly from the age of 6 months on can reduce the risk by up to 78 percent. Sun block -- or sunscreen -- itself poses some minor risks, the Minnesota Poison Control System explains, but they are offset by the benefits.
Definition
Sun block is a common over-the-counter product that blocks out some of the sun's radiation, which takes the form of ultraviolet rays. UVA rays cause sunburn, while both UVA and UVB rays contribute to skin damage, premature aging and skin cancer. Sun block typically contains inorganic chemicals -- like zinc oxide or titanium oxide -- that scatter or reflect UV rays and organic substances -- like octyl methoxycinnamate or oxybenzone -- that absorb and safely dissipate them.
Time Frame
Health professionals recommend putting on sun block half an hour before going outdoors and reapplying it regularly. To determine when to reapply sun block, multiply the SPF factor with the amount of time it takes for the skin to burn without protection. For example, a person who burns within 20 minutes in the sun will get 400 minutes of protection from SPF 20 sun block. This is only true of products up to 45 SPF, after which the protection time does not increase. A good general rule is reapplication every two hours or after swimming, using a towel, exercising or perspiring heavily. Waterproof sun block offers longer protection during swimming than water-resistant varieties.
Considerations
Expired sun block is not dangerous, according to the University of Connecticut Health Center, but it may have lost its effectiveness. Users may be exposed to unsafe levels of UVA and UVB rays if they apply outdated products.
Alternatives
The FDA recommends protective clothing in addition to sun block as added protection from the sun's rays. Wear wide-brimmed hats, sunglasses and dark clothing with tightly woven fabric for the highest level of safety. People with sensitivities to sun block should always were appropriate clothing while in the sunshine.
Warning
Sunscreen is considered to be safe when used as directed, although it can be harmful if ingested, causing nausea and stomach irritation. It should not be used on babies under 6 months of age and can trigger allergic reactions in certain people. Some products contain compounds like alcohol, lanolin, scents and preservatives that can irritate eyes and skin. Nitrosamine, an ingredient in certain sun blocks, may cause cancer, but the Minnesota Poison System states the amount contained in commercial products has not been shown to pose a safety risk.
