In vivo evaluation of unbound water accumulation in stratum corneum. The influence of acute skin irritation induced by sodium laurylsulfate.

In a series of previous experiments, we showed that the inflammatory response associated with skin barrier function damage induced by sodium laurylsulfate (SLS) was correlated with the concentration of SLS and with the duration of application under occlusion of the surfactant. In this experiment, we measured accumulation of unbound water that occurred when occlusive contact was maintained during a short period of time between the skin and the probe head of an electrometric device. Accumulation of unbound water was expressed as area under the curve (sum of increments of skin capacitance during a 45-second period of time; AUCC). For comparative purposes, we also measured transepidermal water loss (TEWL). Both skin function parameters were established for each individual skin site before and 24 h after removal of SLS patches (10, 5, 1 and 0% control solution under occlusion for 48 h). After SLS insult, AUCC and TEWL were increased, and changes were related to SLS concentration (p less than 0.0002). There was a linear correlation between AUCC and log TEWL (p less than 0.0002). On normal skin before application of SLS both parameters were also correlated (p less than 0.04). The regression line between AUCC and log TEWL of normal skin differed however from that observed on SLS-pretreated sites. This indicates that electrometric data are able to simultaneously characterize changes in skin hydration, a rather static parameter, and changes in the amount of unbound water accumulation (AUCC), a dynamic parameter which proved to reflect TEWL.