Next time youre scanning the aisles for your summer sun protection, consider that producers of five well-known sunscreen brands are facing a class action lawsuit alleging that their claims mislead consumers about their products ability to ward off UV rays and prevent skin damage and cancer.

The suit got us thinking: Are we really clear on what sunscreens can and cant do? Maybe not. So we took some of the biggest claims and ran them by experts. You might want to take what they say—along with the sunscreens they use—to the beach with you this summer.

Myth 1: Sunscreen is all you need to stay safe.
“Sunscreen is only one part of the sun-protection picture,” explains Francesca Fusco, MD, an assistant clinical professor of dermatology at Mt. Sinai Medical Center in New York. “Just slathering it on and doing nothing else isnt going to cut it because, even with sunscreen, theres still up to a 50 percent risk that youll burn.” You also need to seek shade between 10 a.m. and 4 p.m. when sunlight is strongest; cover up with clothing, a broad-brimmed hat, and UV-blocking sunglasses; do regular skin self-exams; and get a professional skin evaluation annually.

Myth 2: SPF measures levels of protection against both UVB and UVA rays.
The SPF (sun protection factor) measures only the level of protection against UVB rays. But several of the 16 active ingredients approved by the Food and Drug Administration (FDA) for use in sunscreens also block or absorb UVA rays, says Warwick L. Morison, MD, professor of dermatology at Johns Hopkins Medical School and chairman of the Skin Cancer Foundations Photobiology Committee. Ingredients include: avobenzone (Parsol 1789), octocrylene, titanium dioxide, and zinc oxide, as well as the recently approved Mexoryl SX. Make sure one of these is in your sunscreen, or look for products labeled “broad spectrum,” which means they protect against UVB and UVA rays.

Next Page: Myth 3: Some sunscreens can protect all day. [ pagebreak ]Myth 3: Some sunscreens can protect all day.
“Regardless of the SPF or what the label says, sunscreens must be reapplied every two hours,” Fusco says. “The active ingredients in most products begin to break down when exposed to the sun.” Only physical blockers like zinc oxide stay potent after two hours, but not all sunscreens are made with these ingredients.

Myth 4: Some sunscreens are waterproof.
The FDA does not recognize the term “waterproof,” so dont count on sunscreen to last through hours of swimming. The agency does recognize “water/sweat/perspiration resistant” (which means a product offers SPF protection after 40 minutes of exposure to water) and “very water/sweat/perspiration resistant” (which means it still protects after 80 minutes). To be safe, reapply sunscreen after swimming or sweating.

Myth 5: A sunscreen can provide “total sunblock.”
“No sunscreen blocks 100 percent of UV rays,” Fusco says. An SPF 15 protects against 93 percent of UV rays, SPF 30 protects against 97 percent, and SPF 50 wards off 98 percent. You should slather two tablespoons on your body a half-hour before going outside, so the sunscreen has time to absorb into your skin.