Photo: paultarasenko (Shutterstock) After spending time in the sun, you’re supposed to reapply your sunscreen every two hours, according to FDA guidelines. But what if you’re not in the sun all the time? What if you used mineral sunscreen, which doesn’t wear out like some types of chemical sunscreens do? Turns out you still have to reapply anyway.
As chemist Michelle Wong explains, reapplying isn’t just about depleting sunscreens, even though some older sunscreen ingredients became less effective as they absorbed sunlight. (Today, however, many chemical sunscreens can handle up to hours of sunlight without breaking down.) There are other reasons as well.
Sunscreen rubs off
Sunscreen is invisible (ideally), so it can be hard to imagine what happens when it’s on your skin for a few hours. For a visual example, consider foundation, the skin-colored cosmetic that forms a base for many face makeup looks. Like a sunscreen, it is meant to be applied in an even layer on the skin. Just like sunscreen, it does not wear out with exposure to the sun or to the air. So what happens when you put on foundation for a few hours? It certainly doesn’t look like new, as it doesn’t magically stay in an even layer on your skin. Every time something touches your face, like your hand or a tissue, a little bit rubs off. (For another cosmetic example, think about how you suddenly have a lot less lipstick on your lips after eating a sandwich.) We might not touch our makeup faces much, but think about how. you apply sunscreen. It’s on your hands, and your hands touch everything. It’s on your legs and the edges of your shorts will brush against it. When you sit in a chair, cavort in the water, or dry yourself off after swimming, sunscreen can rub off. G / O Media may earn a commission
Sunscreen thins and clumps even if you don’t touch it
Okay, but what if you’re sure nothing has touched your face all day? Think, again, of the foundation. You still wouldn’t expect him to be perfect at the end of the day, even if you were very careful. Your skin produces oils and sweat, and you move around too. These factors combine to allow a substance, whether it’s makeup or sunscreen, to migrate around the skin. You’ll end up with bits of sunscreen (or foundation) in the small folds and folds of your skin. Where does this come from? Neighboring skin areas, which now have a thinner layer or not at all, which means that they are no longer sufficiently protected from the sun. In the heat of a sunny day, it happens even more, Wong explains, “It’s worse if there is heavy sweating. Layer [of sunscreen] also breaks and clumps into pieces when your skin moves, when you talk, eat and yawn. Sunscreen can also evaporate in the air and be absorbed into the skin over time, further thinning the layer of product on your skin.
Yes, you need to reapply
Now that you know what happens to sunscreen when it’s been applied to the skin for a few hours, the answer should be obvious: Yes, all kinds of sunscreen need to be reapplied. Not because the sunscreen has run out, but because protection depends on having an even layer of product on your skin. FDA guidelines recommend reapplying sunscreen every two hours, or “more often” if you’ve been sweating or swimming. Water resistant sunscreens are rated for 40 minutes or 80 minutes of water exposure (including sweat), so you can use this as a guideline for when to reapply. It’s also a good idea to reapply if you know you’ve rubbed it. , for example if you wiped the sweat from your face with your sleeve while jogging in the neighborhood. .