THE EFFECT OF HEAT, pH AND ORGANIC SOLVENTS ON THE ELECTRICAL IMPEDANCE AND PERMEABILITY OF EXCISED HUMAN SKIN

SUMMARY.— The permeability of excised human skin to dimethyl sulphoxide and the effects of this solvent on water permeability are described. The results of measurements of the electrical impedance of excised human skin both before and after chemical and heat treatments are also given. Stratum corneum is shown to undergo irreversible structural changes when heated above 65°C. or incubated in aqueous media at pH < 3 or > 9. Simultaneous measurements of water permeability and electrical impedance of skin samples subjected to treatments with dimethyl sulphoxide, detergents and surfactants show that there is a good correlation (coefficient - 0·78) between the two quantities. Some organic solvents including aliphatic acids, bases, and neutral compounds are shown to produce large changes in electrical impedance, and hence, it is inferred, in water permeability. It is suggested that these changes are due to solution of skin components, loosening of the skin structure, and hence swelling and hydration of the skin. The solvent induced changes in water permeability provide an explanation for the accelerating effect of the solvents on the penetration rates of topically applied drugs.