New Rules for Sunscreens

If you use sunscreens, be sure to reapply them frequently. Many sunscreens contain the filters octylmethoxycinnamate, benzophenone-3 or octocrylene, which reflect ultra violet rays away from your skin to protect it only when they are on the surface of the skin. However, when these sunscreens are absorbed and the skin is not re-coated, they increase skin production of harmful oxidants that can cause skin aging and cancer (Free Radical Biology & Medicine, September 2009). Reapplying the sun screen so some remains on the skin's surface can prevent this damage.

• Before you go out in the sun, apply sunscreens to the areas with the most exposure to sunlight over your lifetime: the top of your ears, your face, the back of your neck, and your arms and hands. It is the cumulative exposure to UV light that increases skin cancer and aging.

• To meet your daily vitamin D requirements from sunlight, expose your legs or other areas of your body that have received little cumulative sun exposure over your lifetime. Take care to avoid sunburn.

• Reapply sunscreens every hour or two, particularly when you are swimming or sweating.

• Some sunscreens contain stronger UVA filters (avobenzone, mexoryl, titanium dioxide or zinc) that are less likely to be absorbed into the skin. You do not need to reapply these if they leave a visible white paste on your skin. Check the list of ingredients.

A comprehensive review of more than 1000 sunscreens was conducted by the Environmental Working Group in summer of 2009. Their findings, with brand name listings and recommendations, are available at http://www.ewg.org/cosmetics/report/sunscreen09/investigation/summary-of-findings