ABSTRACT
Transepidermal water loss (TEWL) is the outward diffusion of water through skin (1). TEWL measurements are used to gauge the skin’s water barrier function. An increase in TEWL reflects impairment of the water barrier (2). TEWL measurements allow parametric evaluation of the effect of barrier creams against irritants and characterization of skin functionality in clinical dermatitis and in irritant and allergic patch test reactions (3). An evaporimeter determines TEWL by measuring the pressure gradient of the boundary layer, resulting from the water gradient between the skin surface and ambient air. TEWL measurements can be affected by the anatomical site, sweating, skin surface temperature, inter-and intraindividual variation, air convection, ambient air temperature and humidity, and instrument-related variables, to name a few. Although TEWL is influenced by many variables, experiments show that evaporimeter measurements are reproducible in vitro and in vivo (3,4).
