I've heard some sunscreens include ingredients that were created through nanotechnology. Are they safe to use?

The short answer is maybe. One of the most effective UV blockers is zinc oxide -- the white pasty stuff that nobody likes to use. With nanotechnology, manufacturers can now create zinc oxide crystals so tiny they go on clear, though their sun-blocking capabilities remain the same. The problem is, we don't yet have much data on the safety of these minuscule substances. Laboratory and animal studies suggest that nanoparticles, partly by virtue of their size, can damage brain cells and cause precancerous lesions and inflammation of the lungs, for example. NRDC is working with federal agencies and other public interest groups to expand safety testing for nanoengineered products; in the meantime, it may not be a bad idea to avoid products labeled as containing microfine or ultrafine ingredients, including alumina, titanium dioxide, or zinc oxide. Some brands have nano-engineered sunscreens in addition to the old-fashioned stuff, so skip products made with Z-Cote, which is found in some sunscreens made by Dermatone, Australian Gold, NuCelle, AquaSport, and others. Safer bets include California Baby, Aubrey Organics' Titania sunscreen, and Kiss My Face's oat protein formula.

Send your questions to asknrdc@nrdc.org.