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The Dark Side of Sunscreen

The chemical - known as OMC - is found in more than 90 percent of sunscreen products and filters out damaging ultraviolet rays. But scientists at the Norwegian Radiation Protection Authority found when they combined OMC and simulated sunlight in the lab, it killed animal cells.

"We started this study to find out whether sunscreens were more or less stable after longtime radiation with sunlight," says Terje Christensen, professor and biophysicist with the authority. Instead, they found OMC might do more harm than good.

The team took mouse cells, placed them in an ethyl alcohol solution and added five parts per million of OMC, a lower concentration than found in most sunscreens. Half the cells died. They then exposed the cells to two hours of simulated midday light and found more cells dying. Those cells soaking in a non-OMC solution were alive and well.
"OMC is a very efficient UV filter, it's the most important ingredient you have in the sunscreen," Christensen says. But when combined with light, the byproduct is roughly twice as toxic as OMC on its own.

"We see two types of toxicity," says Christensen. "We can observe necrosis, where the outer cell membrane is disrupted, and becomes less efficient as a barrier. And we can see apoptosis - or programmed cell death - where cells that are damaged by certain substances, will decide by themselves to die; a sort of suicide."

But giving up sunscreen is not the answer, says Dr. Barbara Gilchrest, professor and chair of dermatology at Boston University School of Medicine.

"The fact that it (OMC) may or may not be toxic when placed directly on living cells, seems to me to be quite irrelevant to its effectiveness as a sunscreen ingredient. It's put outside the skin on the dead outer layer of surface, and almost certainly does not penetrate the skin, at least not to any significant degree," she claims.

"I would strongly caution against extrapolating from a cell culture experiment to a clinical-use situation, and I would certainly continue to recommend to my patients that they use sunscreens regularly, including sunscreens with octyl methoxycinnamate in it," she says.

What To Do  
Christensen says he's not telling people to stop using sunscreens; he's just urging them to use other protections. "There are some unknown effects going on, and this is a small alarm bell," he says.

The American Cancer Society estimates more than 1 million cases of skin cancer will be diagnosed this year, and about 10,000 people will die of this cancer.