PBSA is found in about one-quarter of sunscreens and protects skin from harmful UVB rays.

"Consumers should not be terribly concerned about this," said Martin Weinstock, MD, PhD, professor of dermatology at Brown University and chairman of the American Cancer Society's Skin Cancer Advisory Group. He added that what happens in a laboratory test tube doesn't always translate into similar results in the real world, and the study needs to be followed up with more research.

But consumers could use more information about the properties of sunscreen and how their ingredients work. "We need better standards from the FDA on sunscreen use," said Dr. Weinstock. (The Food and Drug Administration handles product package labeling.) Among the information that would be useful would be how long the product lasts on the body and how often to reapply, in addition to the Sun Protection Factor (SPF) already listed on sunscreens.

Several elements affect the viability of sunscreens, said Dr. Weinstock. For example, how well sunscreen adheres to the skin is known as substantivity, while photostability refers to how stable the formula is on skin in the sunlight. Some compounds may react with the sun in the process of absorbing harmful rays, causing these compounds to break down over time.

Current information shows that the value of sunscreen in reducing skin cancer risk by blocking ultraviolet radiation clearly outweighs the potential dangers suggested by this study. But ongoing research into improving the effectiveness and safety of sunscreens is an important strategy for reducing the incidence of skin cancer.

The best ways to avoid skin cancer are to avoid strong sunlight, especially during the middle of the day and to cover up with clothing and wide-brimmed hats. Sunscreen is recommended to help protect exposed areas of skin, but should not be used as the main strategy for skin protection. Even if sunscreen is used, prolonged exposure to intense sunlight can still be dangerous.