Skin Cancer and Sun Sense : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 3)

For many people, sunscreens are the first line of defense.

"With most sunscreens it's important to apply them before you're in the sun," says FDA microbiologist Jeanne Rippere, who evaluates over-the-counter drugs, including sunscreens. They should be applied liberally, and reapplied at least every two hours (more often if you're sweating) or after swimming or toweling off. Sunscreens are rated by an SPF (sun protective factor) number, which is a multiplier of your skin's exposure time before burning. For example, an SPF of 4 means you can stay in the sun four times longer before burning than if you were wearing no sunscreen. Keep in mind that you can't add SPF numbers. If an SPF 4 product gives you an hour in the sun, reapplying won't give you another hour. Your time's up. If you want longer exposure, next time use a higher SPF before going into the sun.

Something else to remember is that two types of UV radiation reach the Earth, UVA and UVB. Both contribute to skin damage, including skin cancer. There are no "safe" UV rays. But the SPF numbering system was devised as a guide to protect against sunburn, which is caused mostly by UVB. Because sunscreens allow you to stay out in the sun longer without burning, you may be increasing your exposure to UVA.

FDA has not approved a rating system for UVA protection because experts haven't reached a consensus as to what constitutes a good test. FDA is working to develop one, but until such a test exists, there's no way to compare products or verify claims made for UVA protection. Manufacturers are allowed to claim UVA or broad-spectrum protection on a product, as long as it contains an ingredient that absorbs UVA.

The American Academy of Dermatology recommends that everyone use a broad-spectrum sunscreen having an SPF of at least 15, and advises consumers to check for ingredients that screen UVA: benzophenone, oxybenzone, sulisobenzone, titanium dioxide, zinc oxide, and butyl methoxydibenzoylmethane (also called avobenzone and known by the trade name Parsol 1789).

"People should not depend totally on sunscreens," Rippere says.

While sunscreens protect against sunburn, they don't necessarily prevent cancer. If you use sunscreens to spend more time in the sun, your skin could collect about the same total exposure to damaging radiation. So it's still a good idea to stay out of the sun at midday, and to protect yourself with a wide-brim hat and clothing.

Wear Some Shade

Clothing offers the advantages of even, non-sticky protection that you don't have to remember to reapply. But many summer-weight fabrics don't give enough protection. Some are well below the minimum SPF 15 that dermatologists recommend. And fibers like cotton offer even less protection when wet.

"You can't just put on any old shirt and expect it to protect you," says Julian Menter, Ph.D., research professor of medicine at Morehouse School of Medicine in Atlanta, Ga. "Fabrics can differ greatly in their ability to shield you from UV radiation."

The ideal sun protective fabrics are lightweight, comfortable, and protect against exposure even when wet. Clothing that is labeled or promoted as providing protection against the sun or limiting exposure to UV rays is considered a medical device and is regulated by FDA. Sun Precautions, Inc., of Seattle, Wash., has received FDA clearance to market its Solumbra clothing for sun protection and is allowed to claim an SPF of 30 for its products.

In an experiment with mice, Menter and colleagues compared a so-called "typical" summer clothing fabric (a tightly woven cotton used in a gardening shirt) with the Solumbra fabric, a proprietary, tightly woven synthetic. With an SPF of 6.5, the cotton fabric protected mice against short-term UV effects, but it didn't protect against long-term skin damage, including skin cancer. In fact, the incidence of tumors in these mice was comparable to that of the mice who received no UV protection. Mice not subjected to any UV radiation and the mice protected by the Solumbra fabric showed no signs of skin damage.

How do fabrics block UV? "It's a combination of factors — fabric thickness, composition of the fiber itself, and especially tightness of weave," says Deborah F. Lumbardo, an FDA biomedical engineer. Dye can be a factor too, she says.

"But remember that you still need to be using sunscreen on whatever areas are exposed," Lumbardo says.

Inside-Out Protection?

Some studies estimate that diet may be involved in 40 to 60 percent of all cancers. More specifically, a high-fat diet has been implicated in colon and breast cancers. In animal studies, a high fat intake increased the likelihood of skin cancer after exposure to UV radiation, while switching to a low-fat diet after exposure reduced the incidence of skin cancer.

Homer S. Black, Ph.D., a researcher at the Veterans Affairs Medical Center in Houston, and his colleagues found a dietary effect in humans as well. In their study, published in the New England Journal of Medicine, a low-fat diet decreased the incidence of actinic keratosis in non-melanoma skin cancer patients. "The risk factors for actinic keratosis and non-melanoma skin cancer are basically the same," says Black.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.