Why You Should Never, Ever Leave Your Sunscreen Out in the Sun—Yes, Even if You’re at the Beach

You’ve likely heard dermatologists preaching the importance of reapplying sunscreen throughout the day, but have you ever wondered why? Sunscreen breaks down when it’s exposed to light and heat, which means it becomes less effective the more time you spend in the sun. Not only does this degradation happen to the product on your skin, it can also happen to the stuff left in the bottle, which is why you never want to leave your sunscreen sitting out in the sun.

“Sunscreens protect your skin very well, but they do degrade,” says Debra Jailman, MD, a board-certified dermatologist in New York City. “You want to make sure that you don’t keep your product in direct sunlight or excessive heat, because it does break down the chemicals in the sunscreen, and it makes your sunscreen less effective. When they test sunscreens that have been out in the sun all day long, they show degradation. That’s why they started putting expiration dates on sunscreens, and that’s why the FDA warnings are ‘don’t keep it out in the sun, don’t keep this out in heat’ but nobody reads that—and I’m telling you, you don’t even see it.”

Sure enough, the Food and Drug Administration (FDA) requires that all sunscreens read “protect the product in this container from excessive heat and direct sun.” So that means you need to keep your sunscreen tucked away when you’re lounging at the beach or a park this summer.

“If you have a cooler with your cold drinks, it’s a good idea to keep your sunscreen with the cold drinks,” says Dr. Jailman. “You could also put it under a towel or put it in your bag.” The key is avoiding direct sunlight.

Doing this will ensure that your sunscreen provides optimal protection, but only if you remember to put it back on. Packing your sunscreen away after use may create an out-of-sight-out-of-mind scenario, so do what you can to stay on top of your re-ups. Maybe you set an alarm on your phone or use your finger to write a little reminder in the sand. Whatever you’ve got to do, do it.

Learn how to find the best sunscreen for your skin:

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