The Facts: A sunscreen's effectiveness is measured by its sun protection factor (SPF)-a number that indicates how long it would take for UVB light to redden skin versus no protection at all. The SPF number, however; doesn't rate any UVA-shielding benefits-and UVA waves make up 95 percent of the Earth's solar radiation.
The Bottom Line: UVA rays are as dangerous as UVB rays and are present year-round. They penetrate through glass and clouds, and damage skin without leaving a telltale burn behind (but will leave fine lines and wrinkles). Look for a sunscreen with "broad spectrum protection" and scan the ingredient list for FDA-approved UVA guards including titanium dioxide, zinc oxide, avobenzone, and oxybenzone.
The Facts: Common outdoor activities such as walking the dog may seem harmless, but any time spent outside unprotected has cumulative, harmful effects, cautions Dr. Henry W. Lim, chairman of the dermatology department at Henry Ford Hospital in Detroit.
The Bottom Line: For everyday incidental exposure, SPF 15 is fine. If you're sitting out or playing in the sun, use at least an SPF 30.
The Facts: Most people don't apply enough sunscreen or reapply it often enough, says Dr. Susan Chon, associate dermatology professor at the University of Texas M.D. Anderson Cancer Center. To get the level of protection listed on the bottle, you'll need one ounce (a shot glass) for the entire body and a teaspoon for the face. Reapply every two hours and after swimming or excessive sweating.
The Bottom Line: Applied properly, an 8-ounce bottle provides only 5 to 7 whole body applications.
The Facts: A regular white cotton shirt only provides an SPF of 5 to 7 (wet it drops to 3).
The Bottom Line: If you can see through a garment when you hold it up to a light, then UVA radiation can penetrate through it.
The Facts:"People fear losing their eyesight above any other sense," says Arizona-based optometrist Stephen Cohen, past president of the Arizona Optometric Association. "When outdoors, wear a wide brim hat and sunglasses with UV protection."
The Bottom Line: Just because sunglasses are dark, doesn't mean they'll save your eyes. Look for a sticker designating 95 to 100 percent UV protection.
The Facts: The light used in tanning beds emits UVA radiation at strengths that, in some cases, are 15 times more powerful than the sun, explains Dr. Dale Abadir, a Rye Brook, New York-based dermatologist and spokesman for The Skin Cancer Foundation.
The Bottom Line: Exposure to tanning beds before age 35 increases your risk of melanoma by 75 percent. It makes you two and a half times more likely to develop squamous cell carcinoma and one and a half times more likely to develop basal cell carcinoma. "The UVA radiation emitted from tanning beds exponentially increases your chances of developing a malignant melanoma," says Abadir.
The Facts: Melanoma is the most dangerous form of skin cancer, but it rarely strikes without warning.
The Bottom Line: Most skin cancers are treatable if caught early. Perform your own checks and see a dermatologist at least once a year for a full-body screening.