Dermatologists have found that a surprising amount of sunscreens aren't up to par

Your favourite sunscreen might not be up to the standards set by dermatologists.

A new study out Wednesday in JAMA Dermatology looked at the top 1% of the sunscreens on Amazon that were the most reviewed and the highest rated by customers. Of those 65 sunscreens, 40% didn’t meet the American Academy of Dermatology’s guidelines.

The biggest reason they didn’t fit the criteria? The sunscreens weren’t water resistant.

For example, EltaMD UV Clear SPF 46, the most-reviewed sunscreen on Amazon, did not meet the guidelines because it wasn’t water resistant, though it managed to check off every other box.

The AAD’s three criteria for sunscreen are: Broad-spectrum protection (meaning it protects against both UVA and UVB rays), an SPF that’s at least 30, and water resistance. Having a water resistant formula is important even if not going in the water because it can stay on your skin longer if you’re sweating. Sunscreens that aren’t water resistant will wear off much faster.

So what should you be using?

Ideally, you should pick one that meets the AAD’s three criteria. But beyond that, it’s important to pick one that you like.

“The best sunscreen is the one that you will actually put on your skin,” Dr. Melissa Piliang, a dermatologist at the Cleveland Clinic told Business Insider in June. If you spring for the expensive stuff, but ration it out so you’re not putting nearly enough on, or if it’s gloppy and you avoid putting it on, it’s not doing you any favours. When it comes to spray-ons versus lotions, it doesn’t matter as long as you’re OK with how it feels on your skin.

That’s something the study found too. Among the sunscreen reviews, “cosmetic elegance,” or how well the sunscreen went on without feeling oily or leaving a residue, was the feature that got the most positive commentary.

Disclosure: Jeff Bezos is an investor in Business Insider through hispersonal investment company Bezos Expeditions.

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