Prediction of susceptibility to an irritant response by transepidermal water loss.

The roles of the natural permeability of the stratum corneum to water, and the changes in that permeability effected by a single patch test, were investigated as parameters to predict the susceptibility of the skin to repeated exposures of an irritant. One site on the forearm skin of 27 non-atopic healthy subjects was exposed to a 0.5% concentration of sodium lauryl sulphate by a single occlusive 24-h patch. Another site was exposed to a twice daily 4-day repeated occlusive patch with the same irritant solution. The effects were evaluated by transepidermal water loss measurements made prior to the applications (baseline) on day 1 (BASE), following the single 24-h patch on day 2 (SINGL), and following the 4-day repeated applications on day 5 (REPET). Individuals with higher BASE had higher SINGL (R = 0.80, P less than 0.001) and higher REPET (R = 0.76, P less than 0.001). There was also a significant linear correlation between SINGL and REPET (R = 0.63, P less than 0.001). Multiple linear regression analysis of results, however, indicated that a high baseline TEWL is better indication of an individual's increased susceptibility (high REPET) to weak irritants than a high TEWL value following a single 24-h patch test. Baseline TEWL may therefore be used as a reasonably accurate preliminary "predictive" screening test for susceptibility to irritants.