Permeability characteristics of the human nail plate

Synopsis The permeation of chemicals across the nail plate and their consequent effects are discussed in relation to cosmetic toxicity and possible clinical efficacy. The reviewed data are then assessed and placed in context with recent observations on the direct assessment of permeability of the human nail plate. Although marked differences between the diffusional barrier characteristics of nail and stratum corneum are shown, a reasonably unified picture of nail plate permeability is drawn from the collective observations. The cosmetic and clinical implications of chemical penetration of the nail plate are briefly outlined and places where knowledge needs to be strengthened are identified.