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Burning QuestionsAmanda Schaffer talks with readers about tanning and sun exposure.

Posted Thursday, Aug. 16, 2007, at 5:08 PM ET

Slate columnist Amanda Schaffer was online at Washingtonpost.com on Thursday, Aug. 16, to discuss the medical science behind "tanning addiction" and sun damage to skin. An unedited transcript of the chat follows.

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Amanda Schaffer: You're right that vitamin D has important health benefits. In fact, a friend of mine who's a neurologist was telling me yesterday about new evidence that it protects against multiple sclerosis. He said that he and other MS neurologists have gotten in the habit of placing patients (especially female ones) on 1000-2000 IU/day of vitamin D.

But it doesn't take much sun-time to make loads of vitamin D, so basking for hours is unnecessary. Ten minutes of sun a few times a week is probably all you need for normal vitamin D production. And you can always take supplements, too.

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Aspen, Colo.: What is the very best sunscreen, one with the best coverage and least harmful ingredients?

Amanda Schaffer: Tough question. The current regulation of sunscreen labeling leaves a lot to be desired. The FDA is expected to weigh in soon with new rules, particularly for UVA claims. But in the meantime, there's a helpful analysis of different products, including a lot of safety info on Environmental Working Group Web site. (I provide a link to this in my article.)

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Kansas City, Mo.: Can you get a sunburn inside? I'm not kidding. I worked construction during the summers in college so had a lot of exposure. Now when I wear a short sleeve shirt in the summer in my office by the end of the day I feel almost like a light burn on my arms. I have both florescent bulbs and windows facing south (but with blinds down). I've taken to putting on sunscreen and that seems to help. ...

Amanda Schaffer: Well, evidence suggests that UVB light, which causes sunburn, doesn't penetrate glass. So, I'm not sure how to explain your experience. On the other hand, UVA light does go through glass, so if you're using a good, broad-spectrum sunscreen, you're probably doing yourself a favor when it comes to other kinds of sun damage.

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Heliocare: I have a problem with melasma (patches of dark skin) on my face and even SPF 70 with helioplex doesn't protect me. Would Heliocare help with that? How effective and safe is Heliocare in general? Thanks.

Amanda Schaffer: I don't think there is any evidence that Heliocare helps with melasma. There are two small studies suggesting that it can reduce burning and some sun-related DNA damage. But the manufacturer still recommends that it be used in conjunction with sunscreen—not as a substitute. I think that with melasma, you want to be very careful and not do anything to increase your sun exposure.

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New York City: Hi, Amanda. The endorphin research you write about sounds interesting. But if tanning can cause melanoma which kills people, why wouldn't evolution select against this endorphin effect?

Amanda Schaffer: That's a big question. One of the researchers I spoke with, David Fisher of Dana Farber, thinks that the endorphin release probably offered large adaptive advantages of its own. It may have been selected for because it reduced the pain associated with sunburn. Or, it may have helped people living at high latitudes to avoid vitamin D deficiency, by drawing them out into the sun. But at this point, these possibilities are still pretty speculative.

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Gainesville, Fla.: Does sunblock expire? My wife says so, but that stuff is expensive. Thanks.

Amanda Schaffer: I think your wife's right. The active ingredients in many sunscreens do break down over time. So it's worth springing for a fresh tube at the beginning of the summer.

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Amanda Schaffer is a science and medical columnist for Slate and a frequent contributor to the New York Times "Science" section. Her writing has also appeared in the Washington Post, Bookforum, the Wall Street Journal, and Technology Review.

COMMENTS

Remarks from the Fray:

While it's certainly turning into a great industry, UV resistant clothing is pretty much unnecessary for most people, as virtually all fabric that isn't see-through does a reasonably effective job blocking UV. Research shows white t-shirts have an SPF of 7, while darker colors are around 10. If you wear an undershirt and something over it, you're pretty well protected without any special clothing. Common sense tells you the biggest problem is caused by unprotected skin, not by people's clothes letting them down. After all, when was the last time you burned or even tanned noticeably under your clothing?

--Sundown

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