The friction and lubrication of human stratum corneum

In vivo measurements are reported of the lubrication imparted by water, various aqueous media, and some hydrophobic oils, to a glass probe sliding on the inner human forearm. The primary aim of the paper is to show that the tribology of the human skin surface may be satisfactorily interpreted on the basis of precedents developed for the rationalization of frictional data for elastomers and thermoplastics, and selected data are interpreted on this basis. Water itself plasticises the stratum corneum and, consequently, has profound effects on the frictional behaviour. The effective lubrication observed in surfactant solutions can be explained in terms of electrostatic double-layer repulsion between charged layers adsorbed on the contacting surfaces. Viscosity effects associated with conventional hydrodynamic lubrication are demonstrated using topically applied silicone oils.