Transepidermal Water Loss

Measurement of transepidermal water loss (TEWL) is widely used to characterize the water barrier function of skin, both in physiological and pathological conditions, to perform predictive irritancy tests, and to evaluate the efficacy of therapeutic treatments on diseased skin. The measurement of TEWL by the Servo Med evaporimeter is based on the principle of the evaluation of water vapor pressure gradient immediately above the surface of the skin. In the absence of forced convection the human skin surface is surrounded by a water vapor boundary layer. The measurement of TEWL is valid only within the boundary layer of diffusion surrounding the human body. The depth of this boundary is therefore crucial and depends on environmental conditions, but under neutral ambient conditions, this layer is assumed to have a depth of 7 to 10 mm.