15, 30, 50, 70… Which SPF Should I Use?

How much more protection does a 30 SPF offer than a 15? If you guessed twice as much, you’re wrong. An SPF of 15 screens 93 percent of UVB rays, while a 30 screens 97 — just four percent more. “UVB protection does not increase proportionally with the SPF number,” says Dr. Elizabeth Hale of the Skin Cancer Foundation. There’s a large jump between an SPF of 2, which protects against 50 percent of UVB rays, and 15, but after that the increments are small.