MODELING TRANSEPIDERMAL WATER-LOSS UNDER STEADY-STATE AND NON-STEADY-STATE RELATIVE HUMIDITIES

A gravimetric method was used for investigating the effect of relative humidity on transepidermal water loss (TEWL) across piglet stratum corneum. Measurements were made under both steady-state relative humidities (iso-RH%) and under constantly varying relative humidities (non-iso-RH%). It is shown that the TEWL-RH% relationships obtained using the two methods are qualitatively similar. The values obtained using the non-iso-RH% method were consistently higher than those determined with the iso-RH% method. Despite this bias, the non-iso-RH% method provides a rapid means for evaluating the effect of moisturisers on TEWL. Initial results suggest that urea markedly decreases TEWL but that pyrrolidone carboxylic acid has little effect.