No tan is a safe tan; depletion of the ozone layer impairs protective screen against cancer-causing radiation.
To understand why sun damages, says Warwick Morison, M.D., associate professor of dermatology at Johns Hopkins University, think of yourself sitting unprotected on the beach for four hours. This sunbathing process kills skin cells by UV radiation and alters the function of collagen and elastin, the connective tissue in the skin. It also causes blood vessels to dilate. "That's why people turn red," he says. Days after you leave the beach burnt and blistered, you lose a layer of skin as it peels off. You may even freckle as a result of local changes in pigment cells. And those are only the acute, immediate changes.
Even tanning slowly and carefully is dangerous. Darrell Rigel, M.D., clinical assistant professor of dermatology at New York University, Manhattan, maintains, "There's no such thing as a safe tan. That's the key point. You have to think about why you tan. The body senses that it is being injured by UV radiation and to protect itself, it produces melanin." (Melanin is the body's natural sun block, the dark pigment that skin cells produce to block out damaging rays and that cause tanning.)
But further damage occurs at the cellular level, he explains. When the sun hits the skin, the DNA in the skin cells gets distorted. "Think of the DNA in the cell as a spiral staircase," he says. "What happens is that the two chains of the DNA are no longer connected and the stairs go off at a funny angle. Normal people have the enzyme that attempts to repair the damage." But, he adds, the repair is never total; some damage always remains, and it accumulates over the years.
While the immediate harm -- the burning, blistering and peeling -- is painful, what people should fear are the long-term consequences of regular sun exposure and tanning -- those skin and other body changes that may appear as many as 20 or 30 years later, long after even the memories of carefree days of sunbathing have faded. Skin cancer is one consequence.
Most experts attribute the dramatic rise in skin cancers to America's love affair with the sun and to Americans' changed lifestyles that put people outdoors for longer periods, for more months of the year, and often in skimpier outfits that leave more skin exposed.
Skin Cancer Increases
There are three main types of skin cancer -- melanoma, basal-cell carcinoma, and squamous-cell carcinoma. The deadliest of these is melanoma, but squamous-cell carcinoma is also a killer and the most common form of skin cancer among black Americans, reports Ted Rosen, M.D., associate professor of dermatology, Baylor College of Medicine at Houston.
According to the American Cancer Society, more than 600,000 people were diagnosed with basal-cell and squamous-cell carcinomas in 1990, up from 400,000 in 1980. Thirty-five thousand more were diagnosed with melanoma in 1990.
The rate of melanomas has doubled in less than a decade, says Vincent DeLeo, M.D., assistant professor and director of environmental dermatology, Columbia Presbyterian Medical Center, Manhattan. "It's already the number one cancer in young women under 35. And it's increasing rapidly." If not removed in the earliest stages, deadly melanomas do not carry a very good prognosis.
Melanomas can metastasize and appear in many sites, says Paul Bergstresser, M.D., chairman of the department of dermatology, University of Texas Southwestern Medical Center, Dallas. "Or they can migrate down the lymph system and can be in adjacent sites, so even if the original melanoma is removed, others may still be present. Or the original melanoma can be entirely removed and that's it." But, he adds, even someone who has had a melanoma successfully removed remains at risk of developing a second one.
Why is melanoma on the increase? "It has been associated with sun exposure," says Bergstresser, "but the link to sunlight is not as logical. It is more complicated. Indeed, patients with melanomas are more common with more sun exposure in southern latitudes, but, also, melanomas may appear on body sites that are protected. Those people with the highest light exposure appear to have a lower frequency of melanomas than those who get sunlight more episodically," he says. Finally, those people who have had severe sunburns at an early age are also at higher risk for melanomas.
Not all melanomas seem to be related to sun exposure, however. The evidence linking sun exposure to melanoma is the strongest for the least common type of lentigo maligna melanoma. But the cause of melanomas in general, adds Arthur Sober, M.D., associate professor of dermatology at Harvard University, is still a controversial topic.
Sun Ages Skin
Cancer aside, sun exposure also ages the skin.
Premature skin aging follows a certain course, says Dr. Rigel. "At one end of the spectrum, you have freckling, and freckles are a sign of sun exposure. At the other end of the spectrum is skin cancer. These are not two separate processes. In between, you have lines, leatheriness, and precancerous actinic keratosis," he says.
Indeed, remarks Dr. Sober, to convince themselves about how the sun ages, people should look at the skin under the arm or on the buttocks. "It's beautiful, wrinkle-free skin," he says. "You'll see some intrinsic aging -- it's thinner, and it heals less quickly. But if you stay out of the sun from early in life, by middle age you will look younger, perhaps by as much as 20 years."
UV radiation can damage the eye as well. There is data on Chesapeake Bay watermen who spend large amounts of time on the water that show those who worse sun protection developed fewer catadracts, says Vincent Giovinazzo, M.D., member of the American Academy of Ophthalmology's committee on sports ophthalmology and eye safety. "We feel that if you are out in the sun long enough to get a tan or burn, you should be wearing some protection for your eyes," he says.
But not just any sunglasses will protect, no matter how expensive or glamorous they are. Basic sunglass labeling should help consumers make the right purchase. FDA and the Sunglass Association of America have agreed that manufacturers may voluntarily label sunglass products according to the performance standards set by the American National Standards Institute (ANSI) in New York, says Denis McCarthy, chief of FDA's surgical and diagnostic branch.
According to ANSI, sunglasses fall into three categories: cosmetic use -- lightly tinted for wear in mild sunlight, to block at least 70 percent of UVB and 20 percent of UVA; general purpose -- medium-dark tinted for most outdoor use, to block at least 95 percent of UVB and at least 60 percent of UVA; and special purpose -- dark-tinted glasses for intense sunlight, to block at least 99 percent of UVB and 60 percent of UVA.
For the maximum eye protection, however, says Giovinazzo, people need sunglasses that ensure 95 to 100 percent blockage of both UVA and UVB radiation. In addition, "Look for a wide frame that wraps around. Small glasses may be stylish, but they led lots of light seep in," he says. Cost is not a factor, he adds, because even some of the least expensive sunglasses can offer good protection.
Polarized glasses are good for cutting down on glare, but that does not necessarily mean they block out most UV light, nor does the darkness of the lenses in the eye wear mean much about UV blockage.
Finally, recent research shows that UV radiation not only suppresses the immune response of cells in the skin -- which contributes to the growth of skin cancers -- but may also induce generalized immune suppression and have an important impact on how people fight off infectious diseases, reports Margaret Kriple, Ph.D., chairman of the department of immunology, University of Texas, M.D. Anderson Cancer Center, Houston.
Some experts argue that the shorter, more energetic UVB rays -- even though they are responsible for producing melanin and for thickening the skin's outer layer as protection against sun damage -- are more harmful because they damage cell DNA. "If the breaks in the DNA are not repaired correctly, the next generation of cells will have abnormal DNA that may reproduce cancer cells. Or they may just be cells that die," says Bergstresser.
Others, like Rigel, indict UVA, saying that it penetrates more deeply than UVB and it damages the dermis, the inner layer of skin that contains the blood vessels, hair follicles, and nerve endings -- and ultimately this is responsible for skin aging. Further, adds Janusz Beer, Ph.D., D.Sa., of FDA's Center for Devices and Radiological Health, "In our laboratory, UVA is our prime interest ... If we take a cell culture and expose it to UVA radiation, we can see that these cells disintegrate. That may be happening when we are exposed while tanning and it may be happening in the bloodstream ... If what we see happening in our experiments happens in tissue, then you can certainly change much in the blood by disrupting white and red blood cells."
In the end, all experts agree that all sunlight -- whether on the mountains or at the shore, on the equator or up north, at midday or midafternoon, in winter or summer -- has the potential to damage human skin. And that includes artificial sunlight beamed out of the popular tanning devices that people often use year round in the mistaken belief that these devices tan safely. Manufacturers claim that newer models are safe because they emit only UVA radiation. But UVA itself can be damaging, and many of the UVA devices do emit UVB, "and it doesn't take much to cause damage," says Bergstresser.
While some people are heeding the messages about safe sun exposure, most experts acknowledge that many others pay no attention at all. Further, they realized that few people can totally avoid sun exposure. As a universal precaution, then, people should learn to wear a sunscreen regularly, particularly if they plan to spend any length of time in the sun. "You can be certain about it," says DeLeo. "If used correctly, sun blocks will reduce the likelihood and intensity of sunburn by blocking the UVB rays that create burns."
"Consumers can expect to get the kind of protection the labeling specifies," says William Gilbertson, Pharm.D., director of FDA's division of OTC drug evaluation. Generic sun blocks are just as safe as brand names he continues, but urges consumers to be aware of product differences. Sunscreens are formulated differently so they may affect people's skin differently, he says. He also suggests that people buy a small container of sunscreen to start out -- that way, they can determine whether the product feels good or irritates the skin.
Figuring out which sun protection factor (SPF) of sunscreen to use is an individual decision, says John DiGiovanna, M.D., investigator in the dermatology branch, National Cancer Institute in Bethesda, Md. "The best way to judge the number? For example, if you select an SPF of 15, realize that that means you can stay out in the sun 15 times longer than if you were wearing no sunscreen, and still get the same amount of redness," he says. "Most importantly, you should find something that feels comfortable -- a solution, lotion or cream -- and apply it daily before you go out. Many women recognize that this is the way to prevent photo-aging and they will use a sun block before they put on their makeup."
The American Academy of Dermatology and the National Institutes of Health agree that people should wear a sunscreen with an SPF of 15 or higher. But some experts wonder if sunscreens with SPF higher than 30 really make any sense. Even though the risk of skin cancer for naturally brown- and black-skinned persons may not be as great as for light-skinned individuals, those with dark skin should also apply sunscreens, especially during long periods of sun exposure.
Children should also wear sunscreens. "Most skin cancers begin in childhood," says Sydney Hurwitz, M.D., clinical professor of dermatology and of pediatrics, Yale University School of Medicine. "And the greatest exposure -- 50 to 80 percent of a person's lifetime exposure -- to the sun occurs during childhood, by the age of 18." Studies show that a history of painful or blistering sunburn during the first 10 to 20 years of life doubles the risk of skin cancer. "We've got to convince teachers, parents, doctors, coaches, counsellors, and children that protection from overexposure to the sun is important. For children, putting on a sunscreen should be just like brushing their teeth everyday," he says.
To turn the tide against sun damage, people must learn to think of pale skin as attractive, says Michael Pertschuk, M.D., clinical associate professor, University of Pennsylvania, and chief of psychological services at its Center for Human Appearance. As it has in the past, he believes the fashion industry can alter people's behavior. "It's just going to take some time and an awareness on the part of fashion editors that this is an issue," he says. Once convinced about sun damage, people can act in a reasonables way to protect themselves.
In the end, there really is nothing new under the sun, except that perhaps more people are staying out of it, heeding medical warnings such as Bergstresser's: "Less sun is better. No sun is best of all."
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|Publication:||Nutrition Health Review|
|Date:||Jun 22, 1991|
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