How dangerous is that sunburn?
01:20 - Source: CNN

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Two forms of UV rays can damage your skin, causing wrinkles and cancers

SPF isn't about how long you're exposed to the sun; it's a percentage of rays blocked

CNN  — 

Whether you’re preparing for a day at the beach or an outdoor picnic this summer, make sure to put sun protection on your to-do list.

Skin cancer is the most common cancer in the United States, and UV light exposure is its most preventable risk factor. But according to the US Centers for Disease Control and Prevention, in 2014, over a third of adults reported having a sunburn, the skin’s natural response to UV damage, in the previous year.

Here’s what you’ll need to know to protect your skin against damage.

How to prevent sunburn

A common misconception is that the only way to protect against UV radiation is by wearing sunscreen, says Dawn Holman, a behavioral scientist at the CDC’s Division of Cancer Prevention and Control. Instead, she recommends using a “layered approach”: combining sunscreen with staying in the shade and wearing clothing made from tightly woven fabric, sunglasses and wide-brim hats.

UV light comes in two forms: UVA rays, which tend to cause premature aging of the skin known as photoaging, and UVB rays, which typically cause skin cancers and sunburns. SPF, short for sun protection factor, is a measurement of protection against UVB rays without factoring in UVA radiation.

SPF is essentially a calculation of the additional protection sunscreen gives its wearer compared with bare skin, says Dr. Alexandra Kuritzky, a dermatologist in Vancouver and a clinical instructor in the Department of Dermatology and Skin Science at the University of British Columbia.

“It’s a multiplier, and it’s unique to the individual, because if one individual might be able to, say, spend 30 minutes outside before they sunburn, their SPF 30 product, for instance, is going to protect them for longer than it would an individual who burns after 10 minutes with sun exposure,” she added.

But the US Food and Drug Administration cautions against thinking of SPF as relating to time of solar exposure. Rather, it relates to the amount of sun exposure the wearer gets.

SPF recommendations

Another way to think about SPF is as a percentage of UVB rays blocked. An SPF of 15 blocks about 93% of UVB radiation, while an SPF of 30 blocks around 97%. This means the relative benefit of using a higher SPF decreases as the number increases.

Still, the FDA and the CDC recommend choosing a sunscreen with at least an SPF of 15, while the American Academy of Dermatology suggests at least an SPF of 30.

Holman thinks of the FDA and CDC’s recommendation as a bare minimum. “This is a situation where you want to know your skin,” she said, adding that a fair-skinned individual might want to use a sunscreen with an SPF of 30 or 50.

Of course, sunscreen lives up to its SPF only when it is applied correctly, and most people don’t apply enough of it. One ounce of sunscreen, enough to fill a shot glass, is considered the amount needed to cover exposed areas of the body, according to the American Academy of Dermatology. It recommends applying sunscreen to dry skin 15 minutes before going outside.

For spray-on sunscreen, an ounce can be hard to estimate, so Kuritzky says to apply it “as if you’re spray-painting,” making sure to rub it in with your hands afterward and taking care to avoid inhaling the product.

Best sunscreens for your summer

The FDA regulates the wording sunscreen manufacturers can put on their products’ labels, but multiple studies have shown that most consumers don’t know how to decode this language.

When selecting a sunscreen, it’s important to know what type of sun protection the product will give you. “Broad-spectrum” means the product can protect against both UVA and UVB radiation.

You’ll also want to know about when you need to reapply, especially if you’re planning on swimming or sweating. “Water-resistant” means the sunscreen will offer protection for 40 minutes, while “very water-resistant” means twice as long, or 80 minutes. As a general rule, though, the American Academy of Dermatology recommends reapplying sunscreen approximately every two hours. As of 2011, the FDA disallowed manufacturers from labeling sunscreens as “waterproof” because all sunscreens eventually wash off.

Sunscreens may also advertise “physical” or “chemical” protection, which refers to whether they put a physical barrier – such as with zinc oxide or titanium dioxide – between your skin and the sun, or a chemical one – with oxybenzone or octinoxate, for example. While earlier sunscreens provided purely physical protection (think the white cream that lifeguards put on their noses), most modern ones combine physical and chemical protection for aesthetic purposes, Kuritzky said.

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