A new <i>in vitro</i> method for transepidermal water loss: A possible method for moisturizer evaluation

Transepidermal water loss (TEWL) through the ventral skin of the hamster ear was determined using a modified flow-through diffusion apparatus. Tritium-labeled water was allowed to permeate through the dermal/epidermal layers. Water vapor was collected in a closed system by adsorption onto solid anhydrous calcium chloride in a separately attached receiver. The desiccant was removed, dissolved in water, and the radioactivity determined by liquid scintillation counting. The rate of TEWL was determined for various durations of exposure tothe desiccated nvironment, in the temperature ange between 5 and 40øC. TEWL rate reached a maximum one hour after exposure, and then decreased to a steady state with time. TEWL increased exponentially with increasing temperature in accordance with the Arrhenius relationship. An activation energy value of 13 Kcal/mole was obtained. At incubator temperature of 22øC, the rate of TEWL was found to be 152 _+ 14 p,g/cm2/hr, which agrees with previously reported values obtained by in vivo methods of testing. The present echnique is proposed as a rapid in vitro method for measuring TEWL and as a possible pretest for assessing efficacy of potential skin-moisturizing a ents. Four agents were studied for their effect on water permeability. The agents tested were mineral oil, castor oil, sesame oil, and 25% glycerin in water. Skin membranes treated with occlusive agents uch as mineral oil, castor oil, and sesame oil showed a marked decrease in the TEWL rate, while those membranes treated with the humectant, 25% glycerin in water, showed amarked increase in the TEWL rate. Similar results using these same agents have been reported previously.