There are a million and one preconceptions about sunscreen out there. Smells like coconut? Duh. Leaves a white cast on skin? Probably. Tough to rub in? Definitely. The most common one – All SPFs are made equal. While you might already know that there are physical and chemical sunscreens, you may not realize that there’s a big difference between the two – as well as the kind of protection they offer. Here’s how to figure out which you need to be using. It’s actually pretty simple. Chemical sunscreens pack carbon compounds like avobenzone, oxybenzone and octinoxate. These absorb UV rays and convert them into heat, which is then released – no harm, no foul. On the other hand, physical sunscreens contain mineral ingredients such as titanium dioxide and zinc oxide. These sit on top of the skin to deflect and scatter damaging UV rays away from the skin. Sounds like both get the job done but in different ways and that’s true. Kind of. A recent Consumer Reports study found that only 52 percent of all sunscreens offered the SPF protection claimed on the bottle. The worst offender: Physical sunscreens, of which a measly 26 percent actually met their claims. The thinking is that because physical sunscreens rely on creating a protective layer on skin, that layer might be flawed when you’re applying it. If the product is not applied generously and in all places, UV light can get between the molecules. The same goes for chemical sunscreens, but because they’re not reliant on creating an even, thorough layer of blockers, they’re less likely to allow rays to pass. We know what you’re thinking, if physical sunscreens don’t work as well, what’s the point of using them? For one, they tend to be easier on reactive skin. They’re so gentle, in fact, that most baby sunscreens are typically mineral formulas. People with sensitive skin or with skin ailments related to heat, are recommended to use a physical sunscreen, Also, most ‘natural’ sunscreens on the market fall into the physical category – so if you’re a green queen, that might be your only option. But if you have zero preference and just want the best protection, then just layer both. Start with a chemical blocker and add a physical one over it. Then, throughout the day, re-up with the physical sunscreen. It sounds like overkill, but it’ll be worth it when you get to September without a sunburn.