Trans-epidermal water loss (or TEWL) is defined as a measurement of the quantity of water that passes from through the epidermal layer of our skin to the surrounding atmosphere via diffusion and evaporation processes. This is a continuous process over which we have little control. It can increase due to disruption to the skin barrier (wounds, scratches, burns, exposure to solvents or surfactants, extreme dryness) and is affected by humidity, temperature, season, and moisture content of the skin (hydration level).
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