The answer depends on whom you talk to.
The US Food and Drug Administration classifies sunscreens as over-the-counter drugs, which means they must be approved before they are marketed. In March, 2006, the agency released a statement saying that there is "no reason to be concerned about the use of cosmetics containing parabens."
The key issue is whether parabens, which are chemical preservatives, can seep through the top layer of skin, the dead cells that comprise the thick stratum corneum.
Dr. Barbara Gilchrest, chair of the department of dermatology at Boston University School of Medicine, says it can't. The skin "is an excellent barrier," said Gilchrest, who is also a scientific advisor to Coppertone, a sunscreen manufacturer.
But some people are concerned. Parabens, are "endocrine disrupters," which means if they do reach the inner layers of skin, they could potentially damage the reproductive system, said Jane Houlihan, an environmental engineer and also vice president for research for the Environmental Working Group, a not-for-profit environmental advocacy organization.
Her group has studied ingredients in 1,200 sunscreens and found that 64 percent contain one or more parabens.
In a study published in March, chemist Antonia M. Calafat at the Centers for Disease Control and Prevention found that a different ingredient in sunscreen, oxybenzone, does show up in the urine of 97 percent of the 2,517 people she studied. But her study was not designed to determine how this chemical got into the body, via the skin or some other route.
Asked by phone if sunscreens are safe, she said, "I don't think we can tell. Additional research is needed."
It's theoretically possible, said Gilchrest, that minute amounts of sunscreen could pass through the stratum corneum in children because that layer is a less effective barrier than in adults.
But the far greater danger, for children and adults, is insufficient sunscreen use, leading to permanent DNA damage, not the theoretical possibility of harm, she said. This is especially true for fair-skinned people who sunburn easily.
So, use sunscreens. And if you're worried, read the label and don't use those that contain parabens.
E-mail health questions to email@example.com.