9 Things You Didn't Know About Your Sunscreen

In theory, sunscreen should be an uncomplicated affair: If you slather it on every day, you’re protected, and if not, you’re not. Simple, right?

Yet somehow, there are so many factors that make things rather confusing. For example, what is the difference between chemical and physical formulas? SPF 100 is way better than SPF 30, right? Is this bottle I bought two years ago still any good? Hold up—how does this stuff actually work, anyway?

You’re not alone—these are things we’ve pondered ourselves. So to clear things up, we’re tackling some of the biggest FAQs about SPF, as well as facts you’ve probably never even considered. Get the answers to your burning questions (see what we did there?) below.