Danger Under the Sun : Health: Heeding dire warnings, we smear on sunscreens to filter UV-B rays. So why are skin-cancer rates rising? New studies blame UV-A rays--the ones few products are designed to block.
For decades, doctors and the cosmetics industry have encouraged sunbathers and swimmers to use sunscreens to prevent skin cancer. The warnings have been heeded, enough to push sales of sunscreens (sunblocks) and tanning products to a $650 million a year.
Nonetheless, the incidence of skin cancer has grown at an alarming rate. An estimated 700,000 Americans will develop skin cancer this year, many in the 20-40 age bracket that was once largely free of the disease.
Even worse, the incidence of the deadly form of skin cancer known as melanoma tripled between 1975 and 1992. This year, 32,000 Americans will develop melanoma and 6,800 will die, making it the fastest growing form of cancer.
Now, new research may explain this seeming paradox. Most sunscreens protect only against a narrow band of the sun’s rays called ultraviolet-B (UV-B), which creates sunburn and which scientists have long thought to be the sole cause of skin cancer.
This summer, however, researchers at Brookhaven National Laboratory in New York reported that a different, more abundant form of sunlight called ultraviolet-A (UV-A) is equally important in causing cancer.
UV-A does not cause sunburn and has long been thought benign to the skin. In fact, it is the wavelength of light that is used in commercial tanning booths to produce an artificial tan. A sunscreen that only protects against UV-B may increase the risk of cancer among users “because it gives them the confidence to stay in the sun longer,” says biologist Richard B. Setlow of Brookhaven.
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Before this concern arose about the role of UV-A in skin cancer, conventional explanation attributed the rise in melanoma among Americans primarily to changes in lifestyle.
After World War II, the theory went, much greater numbers of Americans became white-collar workers, limiting the amount of time they spent in the sun. On those occasions when they did go out, they were more likely to develop a sunburn, and repeated sunburn has long been recognized as a cause of skin cancer.
“We know that the more sunburn you have, the greater your risk of melanoma,” says Dr. Darrell Riegel, a dermatologist at New York University. That, scientists said, explained why outdoor workers--who developed a “healthy” tan--rarely developed melanoma.
Sunbathing also became a national pastime after World War II, and women and men began wearing skimpier suits, exposing more flesh to sunlight.
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The idea that UV-A plays a role in the rise of melanoma and that sunscreens might be dangerous was first proposed in 1990 by two epidemiologists at UC San Diego. Dr. Frank C. Garland and Dr. Cedric F. Garland, who are brothers, startled the dermatology community with their proposal that the use of sunscreen was actually increasing the incidence of melanoma and other skin cancer.
The most important parts of their argument were that use of sunscreen prevents the body’s formation of vitamin D, which has been found to protect against melanoma, and that UV-A could itself cause cancer. That conclusion was based largely on controversial studies with mice at the Finsen Institute in Copenhagen.
Finsen researchers had previously shown that the use of sunscreen could delay the formation of skin cancer. The higher the skin protection factor (SPF) number of the sunscreen, the longer the mice could be exposed to UV-B before tumors arose. This research is often cited by supporters of sunscreens as the key evidence of their efficacy.
But the same researchers also exposed mice to small amounts of sunlight followed by exposure to UV-A, a sequence that is common for people using sunscreen. This pattern doubled the number of tumors developed by the mice.
The Garlands concluded that sunscreen use increased the danger of developing cancer. Frank Garland said in 1990: “When you block out ultraviolet-B light, you stop the skin from burning, which means that you can stay out in the sun for many hours or many days. So what happens is you end up getting an unnaturally high dose of ultraviolet-A. Sunscreens give you a false sense of security.”
Dr. Leonard Kurland of the Mayo Clinic in Rochester, Minn., called the Garlands’ analysis “intriguing and worth exploring further,” but other researchers scoffed, particularly because the Garlands offered no hard evidence that UV-A could cause melanoma.
They were also chided for grandstanding because their conclusions, presented at a scientific meeting, were picked up by the media and highly publicized before they were published in a scientific journal.
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Stung by the criticism and fearful that grants for their other research would be adversely affected by further publicity, the Garlands have subsequently refused to talk to journalists about sunscreens. But they seem to have won a vindication of sorts as the result of Setlow’s studies.
Setlow works with a specially bred strain of fish that carries tumor suppressor genes, identical to those in humans, that prevent melanoma until the genes are damaged by ultraviolet radiation. Humans who inherit a defective form of this gene are 1,000 times more susceptible to melanoma than are healthy individuals.
Because the fish genes are the same as those in humans, “you’d naturally suspect that whatever causes melanoma in (them) would cause melanoma in a human,” Setlow says.
Setlow reported in the July 15 Proceedings of the National Academy of Sciences that 38 of 85 fish exposed to UV-A developed melanoma. Also, 30 of 124 fish kept in an aquarium in a glass greenhouse--which blocked UV-B from sunlight--developed melanoma. Even 18 of 61 fish exposed to violet (or visible) light developed tumors. But only one of 20 control fish kept in an aquarium that was bathed in subdued yellow light developed tumors.
Scientists had previously believed that UV-A and visible light did not damage DNA. “But our work shows that something is happening in response to these wavelengths to damage DNA,” Setlow says.
Those findings “certainly raise concern” about the role of UV-A in the development of melanoma, says medical geneticist Michael Siciliano of the University of Texas-M.D. Anderson Cancer Center in Houston, who has worked with the specially bred fish. “What you find in the fish should be applicable to all vertebrates. It’s very valid.”
Not everyone agrees, however. “It’s a big leap of faith to go from a fish model to humans,” says Dr. Merrick Ross, an oncologist at the Anderson Cancer Center. “I think it is a very interesting study and it is very well done, but I’m not personally ready to make that jump.”
Setlow is not willing to go as far as the Garlands in blaming the melanoma surge on sunscreens. “All we are saying is don’t trust a sunscreen unless it says something explicit about UV-A.”
Sunscreens and Skin Cancer
Sunscreen creams and lotions that do not protect against all wavelengths of ultraviolet radiation may be putting people at risk. Melanoma and other skin cancers are on the rise, despite much greater use of sunscreens.
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Increase in rate of melanoma per 100,00 people in the United States-1992: 16.2
First sunscreens introduced: late 1940s.
First effective sunscreen, PABA, introduced: early 1960s.
Note: Figures are age-adjusted
Source: J.T. Flannery, Connecticut Tumor Registry
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ULTRAVIOLET RAYS: Most sunscreens protect the skin by absorbing UV-B, the wavelength of sunlight that causes sunburn. But most do not block UV-A, a different wavelength that new research links to skin cancer. UV-A is used in commercial tanning booths.
SUNBURN: Burning occurs when UV-B destroys the outer layer of skin. Blistering occurs in extreme cases.
SKIN CANCER: Repeated sunburns increase the risk of cancer by triggering replication of the skin. Ultraviolet light can also directly damage the DNA of skin cells. Damage to pigment-producing cells produces melanoma, the more deadly form of skin cancer.
TANNING: Limited exposure to sunlight causes some skin cells to produce a brown pigment called melanin. Melanin acts like a sunscreen, preventing sunburn. But even tanning damages skin.
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TIPS FOR AVOIDING CANCER
* Avoid exposure between 10 a.m. and 3 p.m., when the sun’s rays are strongest.
* Use a sunscreen that protects against both UV-A and UV-B and has a skin protection factor (SPF) between 15 and 30.
* Apply it liberally--one-quarter of a 4-oz. bottle per application.
* Wear long-sleeved shirts and a hat with a broad brim. Avoid artificial tanning devices.
* Remember that temperature has little to do with sun exposure. Ultraviolet radiation is strong on relatively cool days and can penetrate clouds and tree shade.
* Redness and irritation of the skin can occur when patients taking certain drugs, such as ibuprofen and tetracycline, are exposed to sunlight. This can make you more susceptible to sunburn.
* Bronzing creams may make you look tanned, but they don’t provide the same protection from the sun as a real tan.
