However, a study published two months after the USPSTF's analysis was conducted came to the conclusion that sunscreens do prevent melanoma, and many in the public health field felt that it was the most concrete evidence to date that sunscreens are effective. "This is good evidence that sunscreens prevent melanoma, and people should no longer be saying a link has not been shown," says Karen Glanz, PhD, MPH, professor of epidemiology and nursing and Director for the Center for Health Behavior Research at the University of Pennsylvania Schools of Medicine and Nursing. The study, conducted over a 10-year period in Queensland, Australia, followed 1,621 adults who were assigned to two groups: one that applied sunscreen daily and one that applied sunscreen intermittently as the individuals saw fit. A total of 33 melanoma cases arose in the study population, 22 in the intermittent sunscreen users and just 11 in the daily sunscreen users.
Glanz, who also sits on the U.S. Task Force on Community Preventive Services (a partner organization to the U.S. Preventive Services Task Force) says that studies like this one, randomized, controlled trials, are the strongest types of academic studies, and because they're expensive, they aren't conducted very often. "This is the best study we're ever going to get," she says, "and I think it shows that it's really time to lay the question to rest."
Other physicians aren't so convinced. Marianne Berwick, PhD, MPH, professor, chief of the Division of Biostatistics and associate director of population sciences at the University of New Mexico Cancer Center, had issues with the Queensland study, noting that the researchers found lower rates of invasive melanoma, but not preinvasive melanoma. "I would have expected if sunscreens prevent melanoma, they would have prevented both types, but it didn't, and we shouldn't ignore that," she says.
Berwick, a frequent critic of sunscreen companies, conducted her own analysis of sunscreen and cancer literature and published it in the February 2011 issue of Clinical Pharmacology & Therapeutics. In her paper, she concluded that "there is insufficient evidence to suggest that sunscreen use alone is adequate protection against UV radiation." Part of the reason may be the way people actually use the products in the real world. Berwick points to studies showing that people who use sunscreen spend more time out in the sun without reapplying it properly, and that they apply less of it than they should, upping their exposure to ultraviolet (UV) radiation. Furthermore, she adds, most cancers are caused by UVA radiation, rays that sunscreens have only recently been formulated to protect against. And there are no adequate measurements to determine how much UVA is being blocked by a particular sunscreen; SPF measurements on sunscreens only indicate protection against UVB rays, which are responsible for sunburns. Though sunburns are an indication of too much sun exposure, she adds, there's no conclusive evidence that sunburns cause cancer.
That means, Berwick says, that we're pouring money into products that may or may not be giving us the protection we expect, while ignoring truly effective sun-protection strategies. Effective or not, sunscreens are so heavily marketed that the public often assumes that they should be our first line of defense against sun damage and the various forms of skin cancer. "Surveys show that more than anything, people rely on sunscreen," says Glanz. "And I do think that that needs to change." Berwick agrees. "Everyone wants to think that there's a magic bullet, or if they just use sunscreen, they can prevent cancer," she says. "And the industry has made a ton of money promulgating this idea."
And people may not be able to rely on dermatologists to help, as they tend to succumb to the inherent problem other doctors face, Glanz says. "People don't get enough time with the doctor, and the doctor doesn't spend as much time counseling and giving advice as is necessary to convince and even educate people about proper protection," she says, like seeking out shade and covering up with hats, long sleeves, and long pants.
Those measures protect everyone against the known cause of melanoma, which is intermittent sun exposure (like that experienced by people who work in offices all day and spend their weekends outdoors). "Seventy-five percent of melanoma cases occur on relatively unexposed sites, like your back or your trunk, which gives support to idea of intermittent sun exposure," Berwick says. Women get more melanomas on their legs and men get it on their backs, she adds, which see more sunlight when you're wearing casual weekend clothing. That may be because our bodies haven't built up adequate defense mechanisms. Studies on people who spend all day working outside, for instance construction workers, show no higher risk of melanoma or squamous or basal cell carcinomas than the general population. "It may be that their bodies develop a natural defense mechanism," Berwick says. "Their skin gets a little thicker and there may be DNA-repair capacity that's built up by continuous sun exposure."
This summer, as you head out to get your weekend intermittent sun exposure, take truly effective precautions against sun damage:
• Dress defensively. What you wear matters. "My first line of defense is a hat and long sleeves and long pants," Berwick says. And despite what the sunscreen makers may say, the Centers for Disease Control and Prevention, the American Cancer Society, and the International Agency for Research on Cancer all agree with Berwick. If you feel like you'd smother in long sleeves on a 100-degree day, look for special sun-protection clothing that's woven in a way that allows the material to breathe and keep you cool while blocking UVA and UVB rays. Another benefit? Hats and parasols keep you from sweating, so there's no risk of sunscreen sliding off your face into your eyes and causing them to sting or burn. Plus, once you've got your clothes on, there's no need to reapply them!
• Select sunscreen carefully. Beyond the fact that they may or may not work, sunscreens can contain harmful active ingredients. Some sunscreens work by employing chemical UV blockers, such as benzophenone or octinoxate, that act as hormone disruptors and exhibit estrogenic activity. Other products utilize physical UV blockers, such as zinc oxide and titanium dioxide, that lay on top of your skin to prevent UV rays from doing any damage. Those blockers can make your skin white, though, so some companies turn them into sunscreen nanoparticles that are so small, they disappear when applied. Nanoparticles can bypass the skin and cause cell and tissue damage, and may cause cancer. Finally, retinol A, added to improve your skin's appearance and sometimes used as a sunscreen preservative, has been shown in animal studies to promote tumor growth.
Check the labels before you buy. Consult the Environmental Working Group's annual sunscreen guide to find products free of these ingredients for those occasions when you can't escape sun exposure.
• Do regular skin checks. "My second line of defense is to put on sunscreen to prevent sunburn, and third, I take a peek at my skin," Berwick says. "People who are aware of their skin for cosmetic reasons halve their risk of dying from melanoma." Keep an eye out for moles that change color or are irregularly shaped, and help your spouse out. Studies have shown that melanoma is more common in men over 50, and older men are more likely to die from the disease than women, Berwick says. Men often don't pay attention to their skin or know the warning signs of melanoma, she adds, and they need an extra push. Backs and scalps are particularly susceptible, since those areas are hard to see.