Nanotechnology is a subject about which we know less than we should, but probably more than we think we do at first glance. Like Defense Secretary Donald Rumsfeld's quot;known unknowns,quot; we have learned enough to know what we should be concerned with. Glimmers of risk cropped up recently...

While one is hard-pressed to name an industry that has not jumped on the nanotechnology bandwagon, the makers of cosmetics and sunscreens have capitalized on nanotechnology more aggressively than any other. The appeal of using nano-sized particles in sunscreens and cosmetics rather than their...