June 6, 1998
The scientific flap over sunscreens and skin cancer
By KATHLEEN FACKELMANN
Today's beaches are jammed with people who rely on sunscreen for a safe tan. Yet epidemiologists note that the rise in sunscreen use has proceeded in tandem with an increase in skin cancers.
Epidemiologist Marianne Berwick of Memorial Sloan-Kettering Cancer Center in New York carefully laid out the data on sunscreen use and skin cancer at the annual meeting of the American Association for the Advancement of Science (AAAS) in Philadelphia last February.
Sunscreens may not protect against skin cancer, including melanoma, the deadliest form, she concluded. "We don't really know whether sunscreens prevent skin cancer," Berwick says. People ought to be cautious about relying on these products, she told those attending the meeting.
The American Academy of Dermatology promptly denounced Berwick's conclusions. In a March press release, it called her message "misleading and confusing." Berwick, the release said, was telling the public that sunscreens "do not protect against melanoma."
Roger Ceilley, immediate past president of the academy calls Berwick "a numbers cruncher," not a doctor. He believes that when people hear a conflicting scientific message, they'll simply eschew sunscreen. "We're going to have millions more cases of skin cancer in the next decade" if people forgo it, warns Ceilley, a dermatologist in Des Moines, Iowa.
Frank Gasparro of Thomas Jefferson University in Philadelphia says the academy had a knee-jerk reaction to Berwick's talk. Gasparro, who organized the AAAS session, says Berwick accurately portrayed the data on sunscreen and skin cancer. Put her conclusions together with basic research on sunscreen chemistry, he contends, and there is good reason for concern about these products.
No one interviewed for this article took a position against using sunscreens. However, Gasparro, Berwick, and others suggest that science doesn't offer any firm answer to the question of whether sunscreens prevent skin cancer. "Let's get the facts," Gasparro says.
In her review of scientific studies on skin cancer, Berwick looked first at four studies of squamous cell cancer, a skin cancer that appears on the head, neck, and arms and is generally not lethal. Two of the studies concluded that sunscreen protected against a skin condition thought to lead to squamous cell cancer. The other two reported that sunscreen did not shield people from this type of skin cancer.
Berwick also reviewed two studies of basal cell carcinoma, another nonlethal skin cancer, at the AAAS meeting. Basal cell cancer, the most common form of skin cancer, also appears most frequently on the head, neck, and arms. Those studies showed that people who used sunscreen were more likely to develop basal cell cancer than people who did not, she told Science News.
She included 10 studies of melanoma, the skin cancer that gets the most attention because of its virulent nature. Melanoma often develops in or near moles on the skin. In later stages, such cancer can be lethal because of its tendency to spread throughout the body.
In five of the studies, people who used sunscreen were more likely than nonusers to develop melanoma. In three studies, including one done by Berwick, no association appeared between sunscreen use and melanoma. In two studies, people who used sunscreen seemed to be protected.
The epidemiological data are all over the map. The question is, how does one interpret these back-and-forth findings?
One view is that such studies simply do not tell researchers much about sunscreen and skin cancer. Richard P. Gallagher, chief of the cancer control research department at the British Columbia Cancer Agency in Vancouver, says that most of the studies on skin cancer were conducted during the 1970s and 1980s on people in their fifties. Companies marketed the first effective sunscreens during the 1960s, Gallagher notes, so participants couldn't have worn effective sunscreens during childhood, when exposure is thought to kick off the events leading to a skin cancer.
Cancer, including skin cancer, develops in a multistep process. In theory, a skin cell first sustains some injury to its DNA. This initial event, when coupled with subsequent injury, results in a cancer many years, even decades, later. Studies of people who have worn sunscreens for decades have yet to be completed.
Researchers who have become concerned about the safety of sunscreens because of the epidemiological studies have suggested several possible ways in which the products may increase cancer risk.
Berwick, for example, thinks that people who use sunscreen stay out in the sun longer. Sunscreens effectively block the ultraviolet B radiation that causes sunburn, Gasparro says, but they don't all shield the skin from potentially harmful ultraviolet A rays. People who use sunscreen for all-day exposure may get enough ultraviolet radiation to damage the DNA in their skin, he says.
"Sunscreen is a help, but it's not an excuse to stay out in the sun," agrees Rosemary D. Cress of the Cancer Surveillance Program in Sacramento. Cress' 1995 study in the May 15 American Journal of Epidemiology showed that women who used sunscreen appeared to be protected from melanoma. Nonetheless, she recommends caution until that finding is confirmed.
If sunscreens don't effectively block harmful radiation, people at high risk of melanoma may be especially vulnerable. Berwick contends that people who burn easily are the ones who rely most on sunscreens to extend their time outdoors.
In a 1996 study, Berwick and her colleagues showed that people with fair hair and complexions were six times as likely to develop melanoma as people with darker skin and hair. In addition, having numerous skin moles increases the risk of this lethal cancer six fold.
While exposure to the sun plays a role in melanoma, Berwick says, underlying genetic factors may also exert an influence on an individual's risk of this cancer.
The pattern of exposure may be important too. After reviewing several epidemiological studies, Berwick suggests that recreational exposure, in which people get too much sun on their occasional day off, may contribute to the epidemic of melanoma cases seen in the United States and other countries.
The scientific debate doesn't appear on the back of sunscreen bottles, so what's the average sun worshipper to do?
"We do know that both [ultraviolet A and ultraviolet B radiation] cause damage" to the skin, Berwick says. "But life causes damage." She recommends a cautious, yet not unreasonable, approach to summer fun.
For anyone who has to be out in the sun, she suggests protective clothing, including hats, to shield the skin. Far from delivering a no-sunscreen message, Berwick recommends such protection when exposure is unavoidable, such as on a visit to the beach.
Ironically, the American Academy of Dermatology takes much the same approach.
Its literature recommends wearing tightly woven clothing, such as a long-sleeved shirt and pants, and using a sunscreen with a sun protection factor of at least 15. The group also advises people to avoid the midday sun.
Some epidemiologists say that message just won't sell to a sun-seeking public. Residents of Vancouver, for example, would have a hard time complying with the skin cancer guidelines put out by the experts. "If you get sunlight 3 months a year, there's no way you're going to be inside," Gallagher says.
Researchers don't know how much sun is required to cause the damage that leads to skin cancer, although they will someday develop a precise indicator of how much exposure is too much, Gallagher says. Until then, sunscreen, a hat, and a liberal dose of common sense appear to be the best protection.
From Science News, Vol. 153, No. 23, June 6, 1998, p. 360.
Copyright Ó 1998 by Science Service.
Also this week:
Scientists are taking a fresh look at how sunscreens block ultraviolet light.
Skin cancer risks increase for Americans
Take a quiz to help determine your risk for developing skin cancer.
Berwick, Marianne. 1998. Sunscreens and skin cancer: The epidemiologic evidence. Meeting of the American Association for the Advancement of Science. February. Philadelphia.
Gallagher, R.P. 1997. Sunscreen may decrease melanoma risk after all. Worldwide Melanoma Update 1:3.
Holly, E.A. . . . R.C. Cress, et al. Cutaneous melanoma in women. American Journal of Epidemiology 141(May 15):923.
1996. Examining skin reduces melanoma deaths. Science News 149(Jan. 20):47.
Cress, R.D., and E.A. Holly. 1997. Reduced risk of cutaneous melanoma among women who use sunscreen. The Melanoma Letter 15:1.
Fackelmann, K.A. 1997. Moles heighten skin cancer risk. Science News 151(June 7):359.
Find more information on skin cancer detection and prevention at the America Academy of Dermatology's "Skin Savvy 98" web page, at http://www.aad.org/newsf.html.
Memorial Sloan-Kettering Cancer Center
1275 York Avenue
New York, NY 10021
6000 University Avenue
West Des Moines, IA 50266
Rosemary D. Cress
Cancer Surveillance Program
2800 L Street, Suite 440
Sacramento, CA 95816
Richard P. Gallagher
British Columbia Cancer Agency
600 West 10th Avenue
Vancouver, BC V52 4E8
Thomas Jefferson University
233 South 10th Street, Room 428
Philadelphia, PA 19107