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Sunny DazeIs tanning addictive? Does sunscreen really help prevent skin cancer? And other burning summer questions.

By Amanda Schaffer
Posted Tuesday, Aug. 14, 2007, at 2:51 PM ET

Amanda Schaffer was online on Aug. 16 to chat with readers about this article. Read the transcript.

(Continued from page 1)

What's going on? Until recently, most of the sunscreens on the market blocked or absorbed UVB but not UVA. (An exception is old-fashioned zinc oxide.) So some experts worry that UVA is the real culprit when it comes to melanoma. And by reducing sunburn, which is caused by UVB, these sunscreens may have allowed sunbathers to stay out longer, increasing their overall exposure to UVA and, possibly, their risk of melanoma.

The implicit lesson, then, seems to be about the importance of developing and using better UVA protection. Some new broad-spectrum sunscreens include UVA protection—Neutrogena and Banana Boat, for instance, are running aggressive ads this summer touting their formulations. (The Food and Drug Administration will soon weigh in with new rules for UVA labeling; in the meantime, for a helpful consumer guide, see here.) It's typically harder to protect against UVA than UVB, so better products are still needed. And in any case, the sun-cancer link is probably more complicated.

In the 1990s, Richard Setlow, a biophysicist at Brookhaven National Laboratory, took hybrid platyfish bred for cancer susceptibility, exposed them to different wavelengths of light, and determined that UVA and visible light were responsible for 90 to 95 percent of the fish's resulting melanomas. Setlow argues that UVA, with its longer wavelengths, is likely to penetrate deeper into skin, causing abnormalities that may eventually result in the cancer. But more recent studies don't support this. In 2004, researchers at George Washington University Medical Center experimented on mice to assess the relative importance of UVA and UVB and found that "only UVB-containing sources initiated melanoma." And this month, scientists at the University of Texas raised questions about whether UVB might be a bigger culprit than UVA even in Setlow's platyfish. It seems that UVA rarely induces melanoma, even in these fish, lead researcher David Mitchell told me. New insights into the DNA damage caused by different wavelengths of light further muddy the connection between UVA and melanoma.

So if UVA doesn't explain why UVB-protecting sunscreens seem powerless against melanoma, what might? It's possible that the lag time between sun exposure and tumor development is longer for melanoma than for other kinds of skin cancer, says Fisher, and so the protective effect of sunscreen slathered on in the 1980s and 1990s may eventually cause a decrease in melanoma, even if it hasn't yet. Spotty sunscreen use is probably a factor, too. Most people don't slop on the recommended amount (a shot glass's worth for an adult) and don't keep reapplying after swimming or sweating. This lack of diligence may have a disproportionate impact on melanoma rates compared with other forms of skin cancer.

3) Can you get sun protection from a pill?

Some dermatologists are betting on sun pills to make up for the flaws in topical creams and sprays. The most promising one—though not a sure bet by any means—is called Heliocare. Manufactured from the extract of a Central American fern, Heliocare is supposed to be taken once or twice a day as an adjunct to creams and sprays. It has some street cred because its active ingredient was championed by Thomas Fitzpatrick, a legendary Harvard dermatologist who helped to develop topical sunscreens in the 1960s. According to his son Scott, whose company distributes Heliocare to doctors in the United States, Thomas Fitzpatrick later came to believe that the topical sunscreens were insufficient, and so he supported the development of a pill and conducted some of the early research on the fern extract. (The elder Fitzpatrick passed away in 2003, so we can't ask him.)

Two small studies, published in 2004 in the Journal of the American Academy of Dermatology, suggest that Heliocare's active ingredient may help prevent sunburn and some of the DNA damage caused by ultraviolet light. In one paper, researchers measured the response of nine people to ultraviolet light before and after taking oral doses of the fern extract. Afterward, participants tended to experience less sunburn, and their skin samples showed fewer cyclobutane pyrimidine dimers, a form of DNA damage linked to skin cancer.

These studies were funded by I.F. Cantabria, the Spanish company that manufactures Heliocare, and they were probably too small to pick up on side effects. Still, Scott Fitzpatrick says, sales are booming, especially in sunny states like Texas and California. Other pills that promise to protect against sun damage are apparently popular in Europe. So expect to see more of these sun busters peeking out of a beach bag near you. Keep in mind, though, that even the best broad-spectrum sunscreen can't beat the old advice: Wear a hat, and keep out of the midday sun.

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Amanda Schaffer is a science and medical columnist for Slate.
Photograph of sunbather by Mario Tama/Getty Images.
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Remarks from the Fray:

When it comes to cause and effect... has any one thought about doing tests on the sunscreens to see if they are imparting cancer causing agents on the skin? Perhaps the reason skin cancer is going up is because the use of sunscreens is going up...dah... it is worth looking into.

Also, what about all those tribesmen that wear very little and are in the sun much of the time? There is also apparently a link between people that burn and cancer risk vs. just exposure alone.

--Randy1111

(To reply, click here.)

(8/16)

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