What You Don't Know About Sunscreen -- And You Should

• By CODY FENWICK (Patch Staff)

With the summer season officially arriving with the Memorial Day weekend, you'll probably be spending more time out in the sun. And if you've been listening to the warnings dermatologists have been stressing for years, this means one thing: lathering on sunscreen.

Sunscreen, though, isn't what it used to be — nor is the advice on how to use it.

“I recommend an SPF of around 30, as long as you’re reapplying it every hour, hour-and-a-half when you’re outdoors,” Lauren Ploch, a dermatologist from the Georgia Dermatology and Skin Cancer Center, said.

This is pretty standard advice, echoing the American Academy of Dermatology's recommendations. SPF, which stands for “Sun Protection Factor,” measures how protective sunscreen is against ultraviolet B (UV-B) light, which is the segment of the sun’s rays that causes sunburns. The higher the number, the more the protection.

But more important than the SPF number are the words "broad spectrum."

While a sunscreen without those words will protect against sunburn, unless that sunscreen also includes "broad spectrum protection," it'll do nothing to protect against ultraviolet A (UV-A) light, which has a much longer wavelength and penetrates deeper into the skin. It can also cause skin cancer.

“What you want to look for is ‘broad spectrum,’” Ploch said. Sunscreen with broad spectrum protection blocks both UV-A and UV-B light, which means you’ll reduce your risk of sunburn as well as skin cancer.

(Sunglasses, too, should be labelled as providing UV-A and UV-B protection as well.)

In 2012, the Food and Drug Administration changed its rules to reflect the importance of UV-A protection. Now, any sunscreen that is SPF 15 or above, and carries the label "broad spectrum," has to provide protection both from both UV-A and UV-B light. Any sunscreen SPF 14 or below, or that isn't labelled "broad spectrum," is primarily only useful for protection from UV-B light and against sunburns.

SPF numbers reflect a simple metric. Supposedly, if you could stay in the sun for 10 minutes without getting a sunburn, a sunscreen with an SPF of 15 would increases the length of time you can stay out in the sun by 15 – so you should be able to stay in the sun for 150 minutes without getting burned.

Yet this is misleading, because dermatologists recommend reapplying sunscreen at least every 2 hours, if not more frequently. So even if a sunscreen with SPF 50 could theoretically protect you for up to 500 minutes, you should still be reapplying after 120 minutes.

This doesn't mean there's no difference between SPF 15 and SPF 50. SPF 50 should prevent more UV light from affecting your skin.

The FDA also suggests that any measurement above SPF 50 is unlikely to be meaningful.

Sunscreen manufacturers are no longer allowed to claim their products are "waterproof," because none truly is. They can claim that their sunscreens are water resistant for either 40 minutes or 80 minutes, after which point the sunscreen should be reapplied.

Yet there's good reason to be suspicious of some of these claims as well. A new study published by Consumer Reports found that nearly half of all sunscreens didn't live up to their SPF label when after users went in the water, even though they claimed to be water resistant.

--Image via Across America Patch