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By Dr. Howard LeWine

Q. I went to buy sunscreen. I spend a lot of time in the pool and wanted to buy a sunscreen that was waterproof. I couldn’t find any. Have the labels changed?

A: Most sunscreen products have new labels.

Mandated by the U.S. Food and Drug Administration (FDA), the new rules should provide more useful information with fewer misleading terms.

“Waterproof” is one of the banned terms, replaced by “water-resistant.” Labels of water-resistant sunscreens must clearly state how long they provide protection after water exposure or sweating. The FDA has also banned the term “sunblock.” Instead, look for labels that state, “broad spectrum.” A broad spectrum sunscreen must pass tests proving that it truly protects against both ultraviolet A (UVA) and ultraviolet B (UVB) rays.

When sunlight hits your skin, it’s being exposed to UVA and UVB rays. UVB rays are the main cause of sunburn, while UVA rays can prematurely age and wrinkle skin. Both contribute to skin cancer. That’s why you always want a broad spectrum product.

Sunscreens vary in their ability to protect against UVA and UVB based on their SPF, or sun protection factor. Sunscreen with an SPF of 15 would prevent your skin from turning red for 150 minutes under the same conditions. You might think that an SPF of 30 would work twice as well, but that’s not necessarily the case. While SPF 15 filters out approximately 93 percent of all incoming UVB rays, SPF 30 filters out 97 percent and SPF 50 boosts that to 98 percent.

The American Academy of Dermatology recommends a sunscreen with an SPF of at least 30. The FDA says you don’t need a sunscreen with an SPF higher than 50.

Dr. Howard LeWine is an internist at Brigham and Women’s Hospital in Boston.