Slate: Does sunscreen really help prevent skin cancer?

[Editor-in-Chief]

Sunny Daze

Is 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.

What's the science behind sun worship?
This summer, science is grappling anew with the burning, beguiling power of the sun. Three investigations worth watching (from under a big leafy tree) focus on whether exposure to ultraviolet light is potentially addictive; why using sunscreen does not seem to be associated with a lower risk of melanoma, the most deadly form of skin cancer; and whether sun protection can come in pill form. All of which may influence what kind of sunscreen you buy, what else you do to protect yourself—and, arguably, why it feels so good to soak up those dangerous rays in the first place. A rundown:

1) Is ultraviolet light addictive?
A fundamental question in sun science is why we go on basking like lizards despite the obvious risks. Researchers have long suspected a connection between UV exposure and natural "feel good" molecules called beta-endorphins, which are also released during exercise. But for years, the evidence was ambiguous, as some scientists looking for it failed to find an endorphin surge in peoples' blood following exposure to ultraviolet light.
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Last year, however, the field warmed up, so to speak. Steven Feldman, a dermatologist at Wake Forest University, gave eight frequent tanners a drug called naltrexone, which blocks the body's opioid receptors. These are sites in the body and brain where endorphins, as well as drugs like morphine and codeine, may attach. Feldman found that on naltrexone, half of the frequent tanners showed signs of withdrawal, like nausea and jitteriness, whereas none of the infrequent tanners did. He argues that with their opioid receptors blocked, the tanners "were deprived of their UV fix," because they'd developed a chemical dependency on the light.

David Fisher of the Dana Farber Cancer Institute in Boston thinks there may be an evolutionary rationale for the sun's draw. Maybe the endorphin release offered an adaptive advantage by reducing the pain associated with sunburn, or encouraged people living at high latitudes to spend time in the sun and thus avoid vitamin D deficiency. This spring, Fisher and his colleagues happened on a molecular connection between UV light, tanning, and endorphin release. In a paper published in March in Cell, they reported that UV damage directly causes the production of beta-endorphin in the skin.

No one knows exactly how this endorphin release might trigger chemical dependency—the molecules may or may not reach the bloodstream. But the door is now wide open to molecular sleuthing. Meanwhile, some indoor-tanning fans are also touting the endorphin findings, since it seems to prove chemically that tanning feels terrific (even as it kills you).

2) Does sunscreen protect against melanoma?
Epidemiological evidence suggests that sunscreen helps prevent squamous cell carcinoma, one of the less lethal forms of skin cancer. But the findings don't hold true for melanoma (subscription required), the really scary kind of the disease, which appears to be rising at a fast rate. In a couple of studies, sunscreen was actually correlated with higher melanoma risk.

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.

Related in Slate
Amanda Schaffer said there might be an epidemic of vitamin D deficiency.
Juliet Lapidos explained how scientists gauge SPF.
William Saletan argued against the war on tanning.
Douglas Wolk found the best sunscreen, and
Emily Yoffe found the best self-tanner.

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[Editor-in-Chief]

the chat room: Real-time discussions with Slate writers.
Burning Questions

Amanda 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.
Amanda Schaffer: Hi everyone, I'm online and looking forward to your questions about sun and tanning.
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Arlington, Va.: Thank you for taking my question. The debate over the reliability of sunscreens for reducing melanoma risk leads to another possible solution: UV-protective clothing. For years my family has worn Australian-made swimsuits and rash guards. They work better than any sunscreen. It would be great if magazines and newspapers featured these items more, instead of launching every summer with another Cute-Teeny-Suits photo spread. Every year, I see a few more of these suits at the pool, especially on children and men, but women have few choices (Lands End, for instance, sells lots of rash guards for children and men but none for women). Maybe we all need to stop relying exclusively on sunscreen—which is poorly regulated and difficult to apply thoroughly—and start thinking of more reliable forms of sun protection.
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Amanda Schaffer: Great point! I'd love to see more fun, sun-protective clothing out there, too, as well as better research on which materials are most effective at screening UV. There's a group in Germany that has done some interesting work on this topic, actually. A few years ago, they studied around 200 different textiles to see which offered the best UV protection. And if I'm remembering right, polyester and various fabric blends did better than cotton or linen. Color made a difference, too. But I'm sure there's a lot more that could be done with this, and it'd be nice to see big clothing companies getting on it.
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New York, N.Y.: The article mentions that it's harder to develop sunscreens that protect against UVA light than UVB light. Why is that?
Amanda Schaffer: A couple of issues: Some of the compounds that we know protect against UVA light break down quickly in the presence of UV light. For instance, we know that a compound called avobenzone protects against UVA but doesn't last very long. Some companies are working on formulations to stabilize avobenzone—one of the things that Neutrogena's Helioplex technology apparently does.
Another issue is that UVA light is closer in wavelength to visible light than UVB is. This means that, in theory, it could be tricky to block or absorb UVA without blocking some wavelengths of visible light. And of course, if a product screens blue or violet light, it might have the wacky side effect of making people look yellow. I'm not sure how large an issue this one is, though it certainly caught my eye when I saw it mentioned!
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Warwick, N.Y.: Is the "high" effect that comes from tanning the similar to the one people get from using a sun lamp to treat SAD (seasonal affective disorder)?
Amanda Schaffer: Yes, I wondered about that too. The researchers I asked thought that the effects were probably different. They thought that light therapy for SAD mainly involves visible light acting through the eyes, rather than UV light being absorbed by skin. Serotonin pathways also seem likely to be involved in light therapy, though I don't think the mechanisms involved are well-understood.
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Brooklyn, N.Y.: Hi Amanda,
As a welder, I often find myself getting mild sunburns from welding. I'm told that the heat of melting steel is about one-sixth the temperature of the surface of the sun. Am I being exposed to UV light? Could I be addicted to welding?
Amanda Schaffer: Hmmm. If you're getting mild sunburns, you probably are being exposed to UV light. I'm assuming you use protective eye gear and wear longsleeves (though I'm sure that's tough when it's 90 degrees out.) As for the addiction question, I guess it's theoretically possible. Do you find yourself getting jittery when you don't get to weld? I'm not aware of any 12-step welder programs, but you might wanna check it out.
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Bellevue, N.E.: "Encouraged people living at high latitudes to spend time in the sun and thus avoid vitamin D deficiency."
In your article, I was looking for some other points, namely the benefits of vitamin D exposure. Did you know that people that are deficient in vitamin D are at a greater risk of getting high blood pressure, type 1 diabetes, breast cancer, ovarian cancer, prostate cancer, cancer of the lymph system, osteoporosis, fibromyalgia, and cancer of the esophagus? Our bodies are designed to be in the sun, hence the opiate effect that you discuss. That is nature's way of making sure that we get enough vitamin D. Where do you think we would be without the sun? I'm sure you can answer that question. Don't scare people out of the sun, instead tell them to use moderation.
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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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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