The Next Asbestos?(The use of nanoparticles.)

It's a common summer scene on beaches around the world. A mother kneels next to her young boy or girl and applies a thick layer of sunscreen to the child's exposed skin. She's probably read about the rise in the incidence of skin cancer and wants to protect her kids from the sun's rays. Thank goodness she doesn't have to spread the thick white goo lifeguards still use on their noses. In recent years, manufacturers have been engineering sunscreens that blend into the skin. How do they do it? By taking the basic sun-blocking ingredients--powders of zinc oxide and titanium dioxide--and shrinking the particles down to nanosize. That way, they keep the sun's rays from hitting the skin but no longer scatter the light.

Perhaps product labels mention these nanotech ingredients. Students in chemist Leslie Petrik's lab at the University of the Western Cape in South Africa are taught to handle nanoparticles as though they were contaminated with HIV--with extreme caution. All nanomaterials are kept enclosed, and workers always wear gloves and masks when handling them. Petrik and other toxicologists don't think sunscreens are quite that dangerous, but they're not convinced they're harmless, either. Nanoparticles--any particle smaller than 100 one billionths of a meter- -are tiny enough to sneak past the body's immune system. They can slip through cell membranes of the skin and lungs. And, more worrying, they can pass the blood-brain barrier. "If a pregnant mother puts on sunscreen, does it get to the fetus?" says toxicologist Vyvyan Howard at the University of Liverpool in England. "I'm not sure that anyone knows." Says chemical engineer Mark Wiesner of Rice University in Houston: "Is [nanotechnology] the next best thing since sliced bread-- or the next asbestos?"

It's not too soon to ask that question. Most people think of nanotechnology as tiny, futuristic self-replicating robots, but nanoparticles are used now in tennis racquets (for extra stiffness), stain-resistant trousers and cosmetics. Products like L'Oreal Plenitude Futur E Moisturizer contain nanocapsules for delivering moisturizer to deeper layers of the skin, and some self-tanning products contain nanoparticles of pigment. Every day, people--mostly women--rub nanoparticles into their skin. L'Oreal and other cosmetics makers argue that they use chemicals, like zinc oxide, that are known to be harmless. Perhaps it is unfair to compare zinc oxide to the kinds of highly reactive nanoparticles Petrik ...