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

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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Washington, D.C.: While a pill to prevent sun damage sounds great, I would really like a topical sunscreen that doesn't need to be re-applied throughout the day. A "put it on once in the morning and get 24 hours of protection" sunscreen, if you will. Do you know if there are any advances being made in the area of making sunscreen last longer and not break down? Thank you.

Amanda Schaffer: Yeah, that would be great, wouldn't it? I do think companies are working on ways of stabilizing the active ingredients in sunscreen to make them last longer. But for now, I think we've got to keep slathering on a fresh coat every few hours or so. Alas.

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Beaver Falls, Pa.: Do you still get Vitamin D benefits from indoor tanning?

Amanda Schaffer: Well, if you're exposed to UV light, your body can make vitamin D. But you really don't need indoor tanning to make that happen. As I mentioned earlier, a few minutes of sun a few times a week is all it takes to make plenty of vitamin D.

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Warwick, N.Y.: If the researchers mentioned here haven't been able to measure elevated endorphin levels in the bloodstream after exposure to UV, how do they explain light addictive behavior? Isn't addiction primarily mediated by the central nervous system?

Amanda Schaffer: That's a great question. Right now, the evidence that UV light causes endorphin release in the skin is very strong. But where the endorphins go and what happens then is a huge, open question. If the endorphins don't leave the skin, I also find it hard to imagine how they could trigger addiction, but who knows?

Interestingly, even if they do enter the bloodstream, it's not whether they are able to cross the blood-brain barrier. One of the researchers I spoke with, Steve Feldman, mentioned this dilemma. He believes that endorphins probably do enter the bloodstream (even if it'll take better studies with more sensitive measures to establish this). And he suggests that maybe they are able to enter the brain only in some people. In theory, these could be the people for whom tanning is potentially addictive. He doesn't have evidence for this, but it's a provocative theory.

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Indy, Ind.: What do those SPF numbers actually mean?

Amanda Schaffer: SPF is a measure of how well a product protects against burning. So, suppose it takes unprotected skin 15 minutes to burn. If a sunscreen with SPF 10 is applied, in theory, it should take 10 times as long (150 minutes) for the skin to burn.

Keep in mind, of course, that those tests are done using a thick layer of sunscreen. Normal usage—plus swimming and sweating—can lower the protective effect. Also, SPF only tells you about protection against UBV, which causes burning, not UVA. So it's a fairly incompletely measure.

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Amanda Schaffer: Thanks, everyone! Great chatting with you this afternoon. And have a wonderful rest of the summer.

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