The barrier component and the driving force component of transepidermal water loss and their application to skin irritant tests.

Objective: According to Fick's law of diffusion, the rate of transepidermal water loss (TEWL) is determined by a barrier component and a driving force component. The objective of this study is to propose novel indicators for the assessment of skin irritation potential from chemicals using these components.

Methods: Before and after acetone/ether (AE), sodium lauryl sulfate (SLS) and nicotinic acid methyl ester (NME) treatments, the apparent mass transfer coefficient of water, K, of the stratum corneum (SC) and the apparent water vapor pressure, P(d), at the interface between SC and epidermis were estimated as measures of the SC barrier and the driving force, respectively.

Results: After AE treatment, K showed marked increase and P(d) remained approximately constant. All participants reacted to NME with erythema and the laser-Doppler flowmetry (LDF) value peaked at around 30 min. While there was a change in P(d), which parallels with LDF changes, K showed little variation. Repeated SLS treatment induced a slight increase in P(d) besides an increase in K. In the meantime, all participants reacted with subtle erythema.

Conclusions: Our results suggest that not only the SC barrier but also the driving force determines variations in the TEWL rates during skin irritant tests. Together, K and P(d) will provide us with invaluable information about skin condition.