Sunscren use has increased dramatically in the last few decades, but skin cancer rates have also gone up.

RODALE NEWS, EMMAUS, PA—It's that time of year when sunscreen advertisements become ubiquitous on television—cute kids prancing on the beach after their mothers conscientiously apply multiple coats of white lotion in an effort, the companies tell you, to protect against sunburns and skin cancer. Sunscreen has become big business. In 1972, sunscreens and sunblocks raked in $18 million. Last year, a single Banana Boat brand product brought in that amount, and the top 10 sunscreen products on the market netted more than $300 million in sales. Yet, as sales of sunscreen have grown, so has the incidence of melanoma, the most fatal form of skin cancer. Among white Americans, for example, incidence rates for melanoma have increased from approximately 8.7 per 100,000 people in 1975 to 25.3 per 100,000 in 2007, according to the U.S. Preventive Services Task Force (USPSTF). Those numbers raise the question, if we're using more and more sunscreen, why haven't those cancer rates gone down?

THE DETAILS: Sunscreens have been around since the 1940s, and it is well documented that they prevent painful sunburns when used according to directions. But in a January 2011 analysis of the five existing studies looking at how effective sunscreens are at preventing melanoma and other forms of skin cancer (squamous cell carcinoma and basal cell carcinoma), the USPSTF concluded that "sunscreen use has no clear protective or harmful effect on the risk for melanoma." They also found few studies showing that sunscreens can prevent basal cell carcinoma, the least severe and most common form of skin cancer, but did find strong evidence that sunscreens prevent squamous cell carcinoma, a harmful but often treatable form of the disease.

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.