It was just the type of event that many in the nanotechnology community have feared -- and warned against. In late March, six people went to the hospital with serious (but nonfatal) respiratory problems after using a German household cleaning product called Magic Nano. Though it was unclear at the time what had caused the illnesses -- and even whether the aerosol cleaner contained any nanoparticles -- the events reignited the debate over the safety of consumer products that use nanotechnology.

The number of products fitting that description has now topped 200, according to a survey published in March by the Project on Emerging Nanotechnologies in Washington, DC. Among them are additives that catalyze combustion in diesel fuel, polymers used in vehicles, high-strength materials for tennis rackets and golf clubs, treated stain-resistant fabrics, and cosmetics. These products incorporate everything from buckyballs -- soccer ball-shaped carbon molecules named after Buckminster Fuller -- to less exotic materials such as nanoparticles of zinc oxide. But they all have one thing in common: their "nano" components have not undergone thorough safety tests.