The role of the skin as a potential route of exposure to nanomaterials is described in the present chapter. We survey the existing literature on various types of nanomaterials with respect to their penetration through the skin and toxicological responses. Most studies suggest minimal skin penetration and little to no systemic exposure. However, studies have also shown that nanoparticle size, shape, charge, surface properties, and vehicle/solvent as well as the choice of animal species are important determinants as to whether or not nanoparticles traverse through the rate-limiting lipid barrier of the stratum corneum. Long-term in vivo studies in animals or humans are needed because in vitro systems and differences in animal species provide limitations for a complete understanding of nanoparticle penetration through the skin.
