From wrinkle creams to wrinkle-resistant pants, products containing tiny manufactured particles have already infiltrated the marketplace. They're among the first commercial uses of nanotechnology -- the emerging field of manipulating matter on a scale so small that new substances can be built from the atomic level up. Nanotechnology is already touted for its use in new super-strong materials, medical treatments, and other areas. Supporters say it is poised to usher in a revolution as massive as the computer age.

Yet even as the nanotech industry rushes ahead, concerns about ultrasmall particles are mounting. A growing number of studies suggest that they could have troubling effects on human and environmental health.

A nanometer is one billionth of a meter, or about the length of 10 hydrogen atoms in a row. Nanotechnology is usually defined as work on a scale of less than 100 nanometers. The emergence of nanotech reflects a growing knowledge of how materials behave at the atomic level, where the laws of nature get quirky and a material's properties (like conductivity and strength) can be vastly different than at larger scales. That's what makes it all so tantalizing to some researchers -- and worrisome to others.

Numerous studies suggest that nanoparticles can be toxic simply because they are so small. Vyvyan Howard, a toxicopathologist at England's University of Liverpool, recently conducted a review of past research studies and found that, at the nano scale, a particle's toxicity is related more to its size than to the material from which it's made. Nanoparticles can be ingested, inhaled, and absorbed through the skin. They also appear to cross the blood-brain barrier, nature's adaptation for blocking foreign substances in the bloodstream from reaching and disrupting the central nervous system.

The most recent concerns have focused on the fullerene, a nanoparticle named after architect Buckminster Fuller, inventor of the geodesic dome. Fullerenes are cagelike molecules formed of the element carbon that look like soccer balls. In a recent study conducted by researchers from Southern Methodist University in Dallas, largemouth bass exposed to these 'buckyballs' in water for only 48 hours developed brain damage tied to the breakdown of lipids, a common cell compound. Although no commercial products now contain buckyballs, some do contain a related substance -- strong, cylindrical, threadlike structures known as carbon nanotubes. Studies have linked nanotubes to lung abnormalities in exposed rats, while noting their ability to penetrate cells.