Sun Smarts: Everything You Need to Know About SPF

By Marissa Gold

We all know that sunblock is a must. But which products really protect against sun damage? What's the difference between UVA and UVB rays? And what does SPF really mean, anyway? To get answers, we asked dermatologist Kenneth Beer, MD, to explain.

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The Truth About SPF

Q. What does SPF (or sun protection factor) really indicate? Does it have to do with how strong the protection is, or how long it lasts?

A. A higher SPF means more protection against UVB rays, which cause sun burning. SPF has no relevance to UVA protection and ONLY refers to UVB rays, so look for ingredients like Mexoryl and Helioplex (more on those later) that provide UVA protection, too.

Next Up: The Minimum SPF to Use

Our Pick: L'Oreal Revitalift UV