Sunscreen 101: 3 principles to protect your skin from the sun this summer

May 28, 2023

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It took a few tries, but we're finally on the cusp of a sunny summer weekend in the Greater Boston area. The temperatures are set to be in the 80s, and the sun is only shining brighter as the days go on.

That brings us to an ever-important topic: sunscreen.

It’s essential to wear sunscreen outside — not only to avoid sunburns. According to the Environmental Protection Agency, too much exposure to ultraviolet (UV) rays can also cause skin cancer, skin aging and weaken your immune system, even on a cloudy day.

But how do you parse through the shelves of options when it comes to sun protection? What’s the difference between SPF numbers — and is one 3-ounce bottle enough to last all summer?

Here are some tips from NPR’s science desk so you don’t get burned:

As long as you avoid mistakes like using an expired bottle, the exact sunscreen you buy isn’t a huge factor.

What does matter is the amount of sunscreen you apply.

Picture a shot glass. That’s how much liquid sunscreen you’ll want to apply to cover your face and body (about 1.5 oz). For just your face, about a teaspoon of sunscreen is recommended.

No sunscreen blocks 100% of the sun’s rays, and the difference between SPF 15 (which blocks 94%) and SPF 30 (which blocks 97%) isn’t that big. If you want to be safe, SPF 30 should be sufficient. Any more than that doesn’t offer much more protection.

It may feel tedious, but a break in the action is worth it to protect yourself against the midday sun. According to the EPA, the sun is most likely to burn you from 10 a.m. to 4 p.m. Sunscreen should be applied every two hours when skin is dry, and especially after swimming or sweaty activity. Water resistant sunscreens can hold up against some sweat, but they’ll still need to be reapplied within 40-80 minutes of being wet, according to the American Academy of Dermatology.

Chemical sunscreens are most commonly presented as sheer facial sunscreens, oils or body sprays, and contain the active ingredients oxybenzone, avobenzone or octisalate. These ingredients absorb the sun’s rays before they reach your skin. But some chemicals — like oxybenzone — are not reef-safe, and in some cases, chemical sunscreens can enter the bloodstream.

Mineral sunscreens usually contain the minerals titanium dioxide or zinc oxide. Most baby sunscreens have a mineral base, which is less likely to irritate sensitive skin. The minerals form a shield over your skin, protecting it from the sun’s rays, sometimes leaving a pasty, white sheen that honestly isn’t too flattering. (But at least you’ll know you didn’t miss a spot!)

P.S. — Remember to take into account your environment: A chemical sunscreen may not be the best for snorkeling in the Great Coral Reef, but I know mine works well on my face when I’m driving to work. Here’s how to choose what’s best for you.

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