Chemical uptake into human stratum corneum in vivo from volatile and non-volatile solvents

Simple, safe and quick in vivo methods for estimating chemical uptake into the stratum corneum (SC) from volatile and non-volatile solvents are invaluable to health risk assessors. This study compares the human in vivo SC uptake of a model compound (4-cyanophenol) from water and acetone using quantitative attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Small areas on the ventral forearms of human volunteers were treated with 4-cyanophenol (CP) dissolved either in water or acetone. After the skin was cleansed of remaining surface CP, SC samples were taken by a standard tape-stripping method. CP concentration profiles across the SC were quantitated by direct measurement of the permeant on the individual tape-strips using ATR-FTIR. Increasing the duration of exposure to CP aqueous solutions resulted in increasing CP uptake into the SC; the kinetics of uptake correlated well with predictive diffusion equations. Increasing the 'dose' of CP in acetone also resulted in increasing uptake into the SC, but uptake eventually plateaued at a maximum level. The amount of CP taken up into the SC from acetone was 2 to 8-fold greater than that from water following similar short-time exposures. These safe, simple experimental methods provide practical and predictive assessments of chemical uptake into human SC in vivo.