Transepidermal water loss

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Transepidermal Water Loss (TWL) or (TEWL) is a term associated with dermatology and connected sciences.

It is defined as the measurement of the quantity of water that passes from inside a body (animal or plant) through the epidermal layer (skin) to the surrounding atmosphere via diffusion and evaporation processes.

Transepidermal water loss in mammals is also known as "insensible water loss" as it is a process over which organisms have little physiological control.

Measurements of TWL may be useful for identifying skin damage caused by certain chemicals, physical insult (such as "tape stripping") or pathological conditions such as eczema, as rates of TWL increase in proportion to the level of damage. However, TWL is also affected by environmental factors such as humidity, temperature, the time of year (season variation) and the moisture content of the skin (hydration level). Therefore, care must be taken when interpreting the meaning of TWL rates.