Despite SPF Levels, UVA Protection Also Necessary
Even with a high level of SPF, sunscreen alone cannot completely protect you from harmful radiation.
Aug 20, 2009
Originally published: Aug 24, 2009
By Christina Unger
Inside Science News Service
 "Photo: NASA/European Space Agency, License: http://www.noaanews.noaa.gov/stories2004/s2335.htm")
WASHINGTON -- In the last of the summer months, many of us are flocking to beaches, pools and sunny vacation spots to soak in the rays. But even if you’ve heeded warnings about the dangers of the sun and slathered on some high SPF sunscreen, you will need more to protect your skin.
"SPF is a 'sunburn protection factor' that really only tells you how much that sunscreen protects you from sunburn," said Dr. Mary Sheu, a dermatologist at Johns Hopkins Cosmetic and Dermatology Center in Lutherville, Md. "It doesn't tell you how much it protects you from skin cancer and tanning and other damaging effects. It also is only a measure of UVB protection -- it doesn't tell you about UVA protection."
The sun's most skin-damaging effects come from two forms of ultraviolet (UV) radiation -- UVA and UVB. Research has shown that sunburn and skin cancer are caused by UVB radiation, which sunscreen is designed to protect against. Recent research, however, shows that UVA rays -- which are not taken into account by SPF levels -- penetrate deeper into the skin and enhance the damage done to cells by UVB, according to the American Cancer Society, giving skin a wrinkly, leathery look.
"No tan is a safe tan," said Sheu. "Unless it's a bronzer from a drug store, all tans are basically an indication that your skin has been damaged, there has been DNA damage and your skin is trying to protect itself from further damage."
While SPF is a reliable measurement of protection against UVB rays, it is necessary to look at more than the SPF rating to ensure protection from UVA radiation as well.
"There are three sunscreen additives the FDA (Food and Drug Administration) approved that protect against UVA: zinc, Mexoryl, and Avobenzone, which are widely available in a lot of common sunscreens," Sheu said. These can be found by looking at the list of active ingredients on the bottle.
Some sunscreens, such as SPF 15 and higher or broad-spectrum sunscreens, provide some protection against UVA wavelengths but do not provide complete coverage. It is important to make sure that your sunscreen has zinc or one of the other additives to ensure complete protection against UVA rays, Check that it has a high enough SPF rating to shield your skin from UVB rays.
“Many people apply a low SPF and think they are protected, but they're not [and] they stay in the sun longer than they would have if they didn't use it,” Sheu said. She recommends SPF 30 for daily use, even in the winter months.
“There’s UV radiation all year round whether it’s overcast, cloudy or even stormy,” she said. “The UV rays can come through the cloud layer 80 percent so there’s still the risk of getting those damaging effects even though it doesn’t seem bright.”
An SPF 30 or higher should be worn for a day at the beach.
“Apply the sunscreen frequently -- it only lasts two to three hours before it wears off, especially if you are sweating or going into the water,” Sheu said. “No sunscreen is truly waterproof -- some are water resistant, but there’s a limit, and it definitely needs to be reapplied.”
If you use a lotion sunscreen, as opposed to a newer spray-on sunscreen, it is necessary to apply the correct amounts each time. A teaspoon amount for the face and a shot glass portion for the rest of the body of an average adult should be used, said Sheu. The spray-on sunscreens need to be applied in adequate amounts as well, thoroughly covering all parts exposed to the sun -- this can be trickier with a spray, Sheu warns, because it is harder to note areas you may have missed. Sheu recommends taking the extra step to rub after spraying the sunscreen to make sure everything is covered.
“This is quite a lot more than what most people apply and that’s where the higher SPF is useful because you can imagine if you use only half the sunscreen you are supposed to, you are getting much less coverage,” she said. In lab tests, SPF 15 sunscreens filtered out 93 percent of UVB rays, while SPF 30 filtered 97 percent and SPF 50 filtered 98 percent, according to the Skin Cancer Foundation.
Another factor in choosing the most effective coverage involves looking for a sunscreen that's been photostabilized. This means that a chemical is added so that the sunscreen absorbs more UV radiation and remains effective for a longer period of time, according to the American Academy of Dermatology.
All sunscreens break down and become less effective, essentially decreasing their SPF and level of UV protection -- which is one of the reasons sunscreen needs to be applied frequently.
Photostability is an important aspect of the formula, no matter whether you use a kind that reflects or absorbs UV rays.
“There are two varieties of sunscreens,” said Sheu. The physical sunscreens, like zinc and titanium, reflect UV rays and work immediately after they are applied. “Chemical sunscreens are the sunscreens that have longer names like Mexoryl or Avobenzone -- those absorb the sun’s rays and convert them from light to heat energy.”
Because chemical sunscreens take at least 15 minutes from the time of application to start working, a good rule of thumb is to wait up to 30 minutes before going into the sun after applying a sunscreen -- many of which combine both chemical and physical shields into one bottle.
“The physical sunscreens are better for people with sensitive skin -- when someone has an allergy to sunscreen, it’s usually one of the chemical sunscreens,” Sheu said.
