What is the difference between SPF 30 and SPF 50+ — and which level of SPF is best?

The number on a sunscreen does make a difference, from SPF 30 and below to SPF 50 and above, even if the difference between the numbers themselves seems minimal. “SPF 30 filters 96.7% of UV rays, meaning it allows 3.3% to reach skin, while SPF 60 filters 98.3% of UV rays, allowing 1.7% through,” explains Steven Q. Wang, M.D., Director of Dermatologic Surgery and Dermatology at Memorial Sloan Kettering Cancer Center in Basking Ridge, New Jersey. “So SPF 30 actually lets twice as much UV reach skin as SPF 60.”

The GH Beauty Lab generally recommends erring on the higher side when it comes to choosing SPF because people often don’t apply the amount of sunscreen recommended to receive the full protection labeled on the product’s packaging (one small shot glass full or two tablespoons of SPF for body and a nickel-sized dollop of SPF for face). “Our tests have shown that people apply about one-third the amount of sunscreen necessary to achieve the SPF listed on the label,” Aral says. “So we recommend using at least broad-spectrum SPF 50 to compensate.” High SPF numbers can give a false sense of security, though, so remember to reapply at least every two hours and after swimming or sweating.

Ready to dive even further into sunscreens? Below you’ll find the GH Beauty Lab’s expert guide to the ins and outs of sunscreen, from the latest news on sunscreen safety to the best-tested SPFs you can buy for face and body.