Dermatologists and the U.S. Food and Drug Administration (FDA) have issued updated guidance on sunscreen use, emphasizing the importance of SPF 30 or higher, broad-spectrum protection, and proper application. Sun protection factor (SPF) indicates how well a sunscreen protects against ultraviolet B (UVB) rays, which are primarily responsible for sunburns.

SPF 30 filters about 97% of UVB rays, SPF 50 filters about 98%, and SPF 100 filters about 99%. According to the FDA, SPF measures how much solar energy is required to burn skin with sunscreen compared to without it. Doubling the SPF number does not double protection, and higher SPF values offer only marginal increases in UVB filtration.

Most people do not apply enough sunscreen, resulting in less protection than the labeled SPF value. Dr. Adewole Adamson, dermatologist and internal medicine professor at the University of Texas at Austin, said, "Lower SPF sunscreens may feel lighter or be easier to wear, but they provide less protection." He added, "The higher the number, the more margin of error you may have if you under apply."

Dermatologists recommend selecting sunscreen labeled "broad spectrum," which indicates protection against both UVA and UVB rays. UVA rays are harmful and have been linked to sunburns, wrinkles, and some skin cancers. For water or sweat exposure, dermatologists recommend using sunscreen labeled "water resistant."

Dr. Marisa Garshick, dermatologist and clinical dermatology professor at New York Presbyterian-Weill Cornell Medicine, cautioned against misinterpreting high SPF labels. "Someone wearing SPF 100 may think they can stay in the sun longer without reapplying, which is not the case," she said. Sunscreen should be reapplied at least every two hours, or immediately after swimming, water activities, or heavy sweating.

The U.S. Food and Drug Administration banned the term "sunblock" in 2011 because no sunscreen can block all UVB rays. Experts also recommend staying out of the sun during peak UV hours, between 10 a.m. and 4 p.m., and wearing wide-brimmed hats, sunglasses, and sun-protective clothing as part of comprehensive sun protection.