A strategy for the assessment of percutaneous absorption

Percutaneous absorption can be a major route of entry into the body and its measurement is a critical part of risk assessment of chemicals contacting the skin. This paper outlines an approach for the assessment of a chemical's ability to penetrate the skin. Analysis of previously reported data has shown that the ability of a chemical to penetrate skin is dependent on its chemical properties. Using computational techniques, the physical properties of chemicals can be calculated and these are used to estimate permeability constants. At present this technique can only give a useful indication of a chemical's ability to penetrate skin. The use of properly designed experiments can improve this first estimation of percutaneous absorption but they can also give misleading results. The essential features of in vitro protocols are discussed. For chemicals shown to have a potential to penetrate skin, in vivo studies may be required for more accurate risk assessments.