Transepidermal water loss
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Transepidermal water loss (TWL or TEWL) is a term associated with dermatology and its 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. TWL 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.
From a clinical standpoint, TWL measurements are of great importance in evaluating skin barrier functionality. Often normal rates of TWL are compromised due to injury, infection and/or severe damage as in the case of burns. Damage to the stratum corneum and superficial skin layers not only results in physical vulnerability, but also results in an excess rate of water loss. Therefore, dehydration, metabolic acidosis, and conditions such as anhydremia or concentration of the blood are often critical issues for healthcare providers to consider in the treatment of burn patients.
TWL is of major concern in public health, considering the relatively high rate of burn incidence among communities in the developing world due to poor quality cooking stoves. Resources for burn care in local clinics are often scarce and depending on the affected surface area, TWL is a major issue that can be overlooked. Furthermore, TWL is also affected by variations in sweat gland activity, temperature, and metabolism. Therefore transepidermal water loss becomes a significant factor in dehydration associated with several major disease states.
There is at present some confusion over the correct acronym for transepidermal water loss, with some references using TWL and others using TEWL. It is thought that TEWL is often used to avoid confusion with "total water loss," a term commonly used in some disciplines.
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