Here's what you should know about picking a sunscreen

Don't let your lack of sunscreen smarts burn you this summer. A new survey in JAMA Dermatology shows that most people lack important sun protection knowledge, and don't understand much of what's written on lotion labels.

According to Dr. Roopal Kundu, one of the study's authors and a dermatologist at Northwestern University Feinberg School of Medicine, a crucial aspect of picking the right sunscreen lies in the difference in UVB versus UVA protection.

SPF (which stands for sun protection factor — something only 43 percent of people in the study knew) measures a sunscreen's ability to filter UVB rays, which are related to sunburn and skin cancer. However, SPF doesn't tell you anything about UVA ray coverage, Kundu says. UVA rays are also related to a increased risk of skin cancer, but are different from UVB rays because they are not filtered by the ozone at all.

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While UVA doesn't cause sunburn, "it really leads to darkening and aging, because it penetrates deeper into the skin and has more influence in the collagen," Kundu said.

The only way to tell if your sunscreen will protect you from UVA rays are the words "broad spectrum." Kundu said she personally uses SPF 30 sunscreen with the active ingredient zinc oxide, a natural ingredient that physically — instead of chemically — blocks both UVA and UVB rays.

Most importantly, Kundu says typical adults should buy water-resistant, broad spectrum SPF 30 sunscreen, and reapply every two hours using the proper amount. "If we can help reduce or spot skin cancer sooner, or be more aware of it, these are the mechanisms by which we can do it," she told TIME.