"The problem is, zinc and titanium are large molecules that create a whitish cast that isn't cosmetically elegant," says Steven Q. Wang, M.D., director of dermatological surgery and dermatology at Memorial Sloan-Kettering Cancer Center in Basking Ridge, N.J.
Over the last few years, however, sunscreen makers have miniaturized (or micronized) zinc into nanoparticles to prevent the lifeguard look.
The downside? Nanoparticles are tiny enough to penetrate skin and enter the bloodstream. Nanotechnology, which is used in diverse applications including medicine, electronics and energy production, is under investigation by the FDA.
"The concern is, nanoparticles can be potentially absorbed systemically and cause problems, such as cancer," Ostad says.
In sunscreens, micronization is considered safe.
"We looked at 16 studies [conducted in Australia and the European Union] and didn't see evidence of skin penetration," Lunder says.
Less safe: avobenzone. This chemical, which is absorbed into the skin, soaks up UVA/UVB rays. But "it's not very stable and breaks down [50%] in one hour," Wang says.
To stabilize it, manufacturers often combine it with octocrylene (an absorber that offers weak sunscreen protection on its own but keeps other ingredients from degrading).
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