Differences in the response of distinct layers of the skin to surfactants were probed using a modification of the Frosch and Kligman soap chamber test. Soap and other surfactant-containing cleansers were applied to the skin for 2 consecutive days. Transepidermal water loss showed that the stratum corneum is readily damaged even by a mild insult when no erythema is induced. A more severe treatment, such as 24-h exposure to a 5% soap solution, induced the maximal level of barrier damage but a submaximal level of erythema. Even 2 days of exposure to 5% soap does not elicit a maximal erythema response. These results suggest that the stratum corneum is more readily damaged than the dermis, which is not unexpected because the stratum corneum is the initial point of contact between surfactant and skin. Furthermore, this study indicates that for discriminating among mild products, when a small degree of irritation is induced, the most effective measure is stratum corneum damage assessed by evaporimetry. However, for evaluating more irritating products, erythema is probably the more discriminating evaluation technique.