For most people, sunscreen is just one of life's many minor inconveniences that are necessary to avoid cancer and scalding pain. But do you really know how it works? It's incredible, if you think about it: smear this goo on, and the sun, which is necessary for life, won't kill you.
Suffice to say that you probably don't know much about SPF, or when you should reapply. Here are some of the biggest myths about sunscreen, dispelled by Dr. Ingrid C. Polcari, an assistant professor in the Department of Dermatology at the University of Minnesota Medical School.
The higher the SPF, the better
SPF means sun protection factor, and the number stands for how long you should be able to hang out in the sun before you burn compared to if you weren't wearing any protection. So if you've got on SPF 15, you should be able to stay in the sun 15 times longer than you would without any sunscreen on at all, says Polcari. Regardless, most sunscreens will tell you to reapply every two hours.
So higher SPFs must mean better protection, right? Well, this is a gray area. The FDA doesn't have enough proof to confirm that sunscreen with an SPF higher than 50 actually provides extra protection, and they actually want to make it against regulations to claim any SPF higher than 50+. Meanwhile, Polcari says that higher sunscreens do offer a very small increase -- SPF 30 blocks out 97% of the sun's UVB rays, while SPF 60 blocks out just 1.5% more. So while you doubled the SPF number, the amount of extra protection you get is minimal. If you're reapplying SPF 30 or higher frequently, you should be in good shape.