Damaging UVA Rays Go
Unchecked By Most Sunblocks
By Paul Recer
AP Science Writer
WASHINGTON (AP) -- Scientists have discovered that wrinkles, sagging and other signs of sun-damaged skin can be caused by ultraviolet A solar rays, a form of sunlight not blocked by most lotions now on the market.
UVA solar radiation turns a natural molecule on the skin surface into a form of oxygen that speeds up the aging of the skin, said John D. Simon, a Duke University biophysicist and the co-author of a study being published Tuesday in the Proceedings of the National Academy of Sciences.
Researchers have long known that sunlight can cause the skin to wrinkle and turn leathery. But experts said the Simon study is the first to show why this happens -- and to link it to UVA rays.
UVA can be blocked by a few sunscreens, including zinc oxide, that white goo that lifeguards and other beach lovers often smear on their noses, Simon said. Some preparations have zinc oxide in a more transparent form, and more advanced products may now be found.
The new study underscores the importance of using a lotion that blocks both types of ultraviolet radiation -- UVA and UVB. Right now, most sunscreens focus on protecting against UVB while doing little to protect against UVA.
Missy Gough of the American Academy of Dermatology said her organization recommends that people use broad-spectrum sunscreens that have a sun protective factor (SPF number) of at least 15.
Consumers should check the label to make sure lotions contain ingredients that protect against UVA, she said. These include bezophenone, oxybenzone, sulisobenzone, titanium dioxide, zinc oxide and avobenzone, a sunscreen chemical recently approved by the Food and Drug Administration and sold under the brand name Parsol 1789.
"This study shows that we have to pay more attention (to UVA) and to find blockers that are more effective in that region" of solar radiation, said Janna P. Wehrle, a research director at the National Institute of General Medical Sciences.
Wehrle, whose organization is one of the National Institutes of Health, called the discovery a major advance in understanding how the sun ages the skin.
Simon's study shows that UVA sunlight is absorbed by urocanic acid, a natural molecule made by the outermost skin cells. The sunlight chemically changes urocanic acid and causes it to create within the cells a type of oxygen free radical, a highly active molecule that can be damaging to cells.
This oxygen radical, said Simon, "degrades collagen and elastin, which are the major molecules that make up the skin. This process accelerates photoaging of the skin."
By degrading collagen and elastin, he said, "you decrease the elasticity of the skin. It makes you look older than you might be."
The oxygen free radicals from urocanic acid also may play a role in skin cancer, but that link has not been proved, Simon said.
"People knew there was something doing damage, but they couldn't find any molecule that caused it," said Wehrle. "By finding this indirect mechanism, with the oxygen free radical, they have shown how light can cause the skin damage."
Although the study did not link the mechanism to cancer, Wehrle said the research "is a warning flag" that will need further investigation.
"Once you have oxygen free radicals loose in the skin, they can damage many things," she said.
Most experts have warned about cancer and skin damage caused by the UVB part of sunlight, Wehrle said. As a result, lotions focus on protecting against that type of solar radiation.
Nobody considered UVA a risk until now," said Simon. "I would expect development of skin blockers against this longer radiation wavelength pretty soon."
For now, both Simon and Wehrle recommended long sleeves and hats for people going into the sun.
"People would do well to stay out of the sun in the center of the day," said Wehrle. "People should be covered more of the time they are outside. Hats are a good idea. Moderation is the key."
Simon said he allows his family "reasonable exposure" to the summer sun and encourages people to wear hats.
People don't need to totally avoid the beach or pool, he said. They should be "respectful, but not fearful of the sun. We've got to enjoy our lives."