Are commercially available nanoparticles safe when applied to the skin?

There are a growing number of commercial uses of nanoparticles which involve direct people contact with the potential for absorption through the skin. Nanoparticles are present in a range of consumer products including colloidal health drinks, carbon fibre sports equipment, sunscreens, cosmetics, electronic products and as antibacterial components of toys, cooking products and wound dressings. Environmental sources of ultra-fine nanoparticles have been present for millennia and anthropogenic sources of similar materials result from industrial processes. Recent technological advances have enabled improvements in both the manufacture of nanoparticles and in the study of their safety. With subcellular dimensions, the physical properties of a nanoparticle cannot be easily predicted from the properties of a microparticle with identical chemical composition. Recent studies in animals and humans have sought to document the safety of consumer nanomaterials. In this article, the safety of such materials is critically reviewed.