According to new research, many people are still puzzled by the wide range of SPF numbers on product labels, and some may not be using sunscreen properly. In a recent American Academy of Dermatology (AAD) survey, only 32 percent of respondents knew that an SPF 30 sunscreen does not provide twice as much protection as an SPF 15 sunscreen. Even more concerning, only 45 percent knew that a higher SPF sunscreen does not protect you from the sun longer than a lower-SPF sunscreen. “It’s important that everyone understands what they are seeing on a sunscreen label,” says board-certified dermatologist Abel Torres, M.D., J.D., FAAD, president of the AAD. “A sunscreen with an SPF of 30 blocks up to 97 percent of the sun’s rays. Higher SPFs block slightly more rays, but a higher-number SPF does not allow you to spend more time outdoors without reapplication; all sunscreens should be reapplied every two hours, or after swimming or sweating.” And while 85 percent of participants in the AAD survey knew that sunscreen needs to be reapplied after swimming, a new study from the Johns Hopkins University School of Medicine, published in the Journal of the American Academy of Dermatology in May, indicates that some people may not be using sunscreen correctly. In studying 758 people with a history of nonmelanoma skin cancer and 34,161 control subjects, the authors found that those with a history of NMSC were more likely to seek shade, wear protective clothing, and apply sunscreen, but they still received sunburns as often as those without a history of NMSC. While seeking shade and wearing protective clothing were associated with lower odds of sunburn, sunscreen use was not. “While it makes sense that people with a history of skin cancer were more likely to practice sun protection, we were surprised to see that their methods were not always effective,” says board-certified dermatologist Anna L. Chien, M.D., FAAD, one of the study’s co-authors. “Our results reinforce the importance of everyone using multiple types of sun protection; people who rely only on sunscreen may not be applying enough, covering all their exposed skin or reapplying often enough to shield themselves from the sun’s harmful UV rays.” The AAD recommends that everyone protect themselves from the sun by seeking shade; wearing protective clothing, such as a long-sleeved shirt, pants, a wide-brimmed hat and sunglasses; and using a broad-spectrum, water-resistant sunscreen with an SPF of 30 or higher, applying enough to cover all exposed skin—for most adults, this is about one ounce, or enough to fill a shot glass. Sunscreen should be applied 15 minutes before sun exposure and reapplied every two hours, or after swimming or sweating.