Fun in the sun means knowing your SPFs

Wednesday , August 06, 2014 - 12:00 AM

The experts wail that we’re a math-challenged nation, so it’s no wonder we struggle with SPFs.

All those pesky numbers clutter up the bottles of the sunscreen we know we need to buy to be sun-safe, but what do they all mean?

If it’s SPF 15, does that mean it lasts for 15 minutes — or 15 hours? Does an SPF of 100 block 100 percent of the sun’s rays? What’s the difference between an SPF 30 and an 85?

“I don’t think ... that many people have a very thorough understanding of what SPF means,” says Douglas Woseth, a spokesperson for the Skin Cancer Foundation and a Salt Lake City dermatologist.

We turned to the experts for some help on decoding the SPFs and slathering on our sunscreen to its maximum advantage.

• What’s SPF stand for? Sun protection factor. Simply put, it’s a measure of how well the sunscreen prevents the sun’s UVB rays from damaging your skin.

• What does the number measure? The period of time the sunscreen protects you from burning. If you put on SPF 15, for example, it will take 15 times longer for your skin to burn than if you had on no sunscreen, Woseth explains. An SPF 30 will prevent burning for 30 times longer.

• So a higher number is better? Not necessarily, says Woseth. The SPF’s efficiency can be confusing because it’s calculated in a controlled laboratory setting, he says, but during everyday usage, all sunscreens will wear off and degrade.

“That’s how it’s tested but it’s not real life,” he says. “A number 60 doesn’t necessarily mean you can be out twice as long as you can with a number 30.”

Also, Woseth says higher numbers, like SPF 100, can be misleading because people may assume such a product provides day-long protection. But all sunscreens, whether they’re a 15 or a 60, need to be reapplied every two hours to work properly.

And by the way, no sunscreen blocks 100 percent of the sun’s harmful rays. An SPF 15 filters out 93 percent of UVB rays, according to the Skin Cancer Foundation, while an SPF 30 blocks 97 percent and an SPF 50 blocks 98 percent.

• Anything else on the numbers? Ogden dermatologist Julie Maughan says the SPF ratings are calculated using 2 milligrams of cream or lotion per square centimeter of skin — “which is a huge amount of sunscreen,” sort of akin to using a whole pat of butter on a tiny piece of bread.

“Only 30 percent of Americans apply as much sunscreen as you need to achieve the SPF listed on the bottle,” Maughan says. “So almost everyone under applies.”

• What’s the recommended SPF? For regular daily activities, Woseth says the Skin Cancer Foundation recommends wearing SPF 15. When you plan on doing any extensive outdoor activities, cover up with SPF 30 or higher.

Maughan says she advises her patients to use an SPF 45 product on their face daily — all year round. Studies have shown most skin damage is a result of daily exposure to the sun, she says, be it going to and from your car, or in and out of the grocery store.

• Can SPFs be too low? You’ll find products rated SPF 4 or 5, but dermatologists don’t advocate their use.

“Anything with an SPF lower than 15 is required to have a warning informing the consumer it will not protect against skin cancer,” Maughan says, citing product guidelines set by the Food and Drug Administration. “Those SPF 8s, they’re not really a sunscreen anymore.”

• What rays do SPFs target? The sun protection factor is aimed at blocking the sun’s UVB (ultraviolet B) rays, which cause sunburn and lead to skin cancer, Woseth says. However, consumers need to know they can also get skin damage, like age spots, wrinkles and even skin cancer, from ultraviolet A, or UVA rays, as well.

When buying sunscreen, always look for a “broad spectrum” product, which protects against both UVA and UVB rays, the Salt Lake City dermatologist says.

Contact reporter Becky Cairns at 801-625-4276 or Follow her on Twitter at @bccairns or like her on Facebook at

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