The chemistry of sunscreen is under scrutiny by the U.S. Food and Drug Administration (FDA), which has proposed updated regulations for a product routinely used by American consumers.

Two Rice University synthetic organic chemists are available to discuss the science behind sunscreen and the FDA's plan to bring those products up to date.

László Kürti, an associate professor of chemistry whose lab designs sophisticated molecular building blocks that simplify drug design, said the FDA study is warranted.

"Sunscreen is extremely effective," he said. "As a person who likes to go to the beach, I know what happens when I don't use it, and I don't think we should doubt the resolve of manufacturers to protect consumers.

"The question is the risk-to-benefit ratio," Kürti said. "The FDA has to think about the chemical ingredients that may interfere with human enzymes and hormones and the potential to trigger side effects. And, of course, like the chemical compounds in other consumer products, the chemicals in sunscreen also end up in the environment."

The potential risk, he said, comes not from the minerals -- zinc oxide and titanium oxide -- that give sunscreen its basic properties, but from the organic chemical compounds that provide extra protection by blocking specific wavelengths of UV light and could be absorbed through the skin.

In the proposed rules, only the two minerals are now considered "generally recognized as safe and effective," or in FDA terminology, GRASE.

"Technically, all new drugs have to go through FDA approval, but there are many chemical compounds, some used since the 18th century, that have shown no ill effect at all," said Zhe Zhou, a postdoctoral researcher in Kürti's lab. "Those are 'grandfathered in' and considered generally accepted as safe because of empirical evidence."

The FDA proposes to remove GRASE status for two organic chemicals, PABA and trolamine salicylate, while studying the other 12 chemicals found in many sunscreens.

"It doesn't mean they are banned," Zhou said. "It just means they need more data to determine whether they should be on the list."

Hawaii, where Zhou earned his doctorate, and Key West, Florida, have already banned sunscreens with two chemicals, oxybenzone and octinoxate, suspected of harming coral reefs.

Kürti said testing each organic molecule in sunscreens according to the same vigorous standard that pharmaceutical companies analyze prescription drugs for FDA approval would be prohibitively expensive.

"The sun bombards us with ultraviolet, visible and infrared light," he said. "These organic molecules have chromophores that absorb certain wavelengths on the electromagnetic spectrum, and with the right combination, they filter out most of the harmful rays.

"If the FDA required the full analysis of these compounds' effects, I think sunscreen would become unaffordable," Kürti said. "You would need a prescription for sunscreen, and you would be paying 300 bucks a bottle. Then we would be really harming people."

For more information on Kürti or Zhou, visit http://kurtilabs.com. To schedule an interview, contact Mike Williams at 713-348-6728 or mikewilliams@rice.edu.

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