What Is SPF? SPF — or Sun Protection Factor — is a measure of a sunscreen's ability to prevent UVB from damaging the skin. Here's how it works: If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer — about five hours. Another way to look at it is in terms of percentages: SPF 15 blocks approximately 93 percent of all incoming UVB rays. SPF 30 blocks 97 percent; and SPF 50 blocks 98 percent. And as you can see, no sunscreen can block all UV rays. However, there are problems with the SPF model: First, no sunscreen, regardless of strength, should be expected to stay effective longer than two hours without reapplication. Second, "reddening" of the skin is a reaction to UVB rays alone and tells you little about what UVA damage you may be getting. Plenty of damage can be done without the red flag of sunburn being raised.
Who Should Use Sunscreen? Anyone over the age of six months should use a sunscreen daily. Even those who work inside are exposed to ultraviolet radiation for brief periods throughout the day. Also, UVA is not blocked by most windows. Children under the age of six months should not be exposed to the sun. Shade and protective clothing are the best ways to protect infants from the sun.
What Type of Sunscreen Should I Use? The answer depends on how much sun exposure you're anticipating. In all cases, a broad-spectrum sunscreen offering protection against both UVA and UVB rays is recommend. Many after-shave lotions and moisturizers have a sunscreen (usually SPF 15 or greater) already in them, and this is sufficient for everyday activities with a few minutes here and there in the sun.
How Much Sunscreen Should I Use and How Often Should I Apply It? To ensure that you get the full SPF of a sunscreen, you need to apply 1 oz – about a shot glass full. Studies show that most people apply only half to a quarter of that amount, which means the actual SPF they have on their body is lower than advertised. During a long day at the beach, one person should use around one half to one quarter of an 8 oz. bottle. Sunscreens should be applied 30 minutes before sun exposure to allow the ingredients to fully bind to the skin. Reapplication of sunscreen is just as important as putting it on in the first place, so reapply the same amount every two hours. Sunscreens should be reapplied immediately after swimming, toweling off, or sweating a great deal.
Once you choose the right sunscreen, use it the right way. But remember, you should not rely on sunscreen alone to protect your skin against UV rays. For more information, log onto The Skin Cancer Foundations web site at www.skincancer.org you will find additional Prevention Guidelines that can lower your risk of developing skin cancer and help your skin look younger, longer.