Transepidermal water loss (TEWL or TWL) is the loss of water that passes from inside the body through the epidermis to the surrounding atmosphere via diffusion and evaporation processes.
TEWL is also known as insensible water loss (IWL), as it is a process over which there is little physiologic control and of which is usually unaware.
TEWL is the passive diffusion of water vapor from the body through the epidermis to the external environment, occurring independently of sweat gland activity.
TEWL is a quantitative measure of the amount of water that evaporates from the skin surface per unit of time
TEWL is widely used as an objective indicator of skin barrier function.
Elevated TEWL reflects impaired barrier integrity, as seen with atopic dermatitis, while lower TEWL is associated with healthy, intact skin barrier function.
TEWL is measured by specialized probes that detect water vapor density at the skin surface: open-chamber, closed-chamber, and condenser-chamber devices.
The measurement is sensitive to environmental factors such as humidity, temperature, and airflow, and varies by anatomical site, age, and skin condition.
TEWL is considered a key parameter in dermatological research and clinical practice for assessing skin barrier status and evaluating the effects of topical agents or disease states on barrier function.
Insensible loss of body water can threaten fluid balance, and dehydration sometimes occurs.
Measurements of TEWL can identify skin damage caused by certain chemicals, physical insults or pathological conditions such as eczema, as rates of TEWL increase in proportion to the level of damage.
TEWL is affected by environmental factors such as humidity, temperature, the time of year and the moisture content of the skin.
TEWL measurements are of great importance in evaluating skin barrier functionality.
Normal rates of TEWL – from 2.3 g/(m2h) to 44 g/(m2h)[3] are compromised due to injury, infection and/or severe damage as in the case of burns causing rates over 50 or even over 100 g/m2/h.
When there is damage to the stratum corneum and superficial skin layers it 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 issues to consider in the treatment of burn patients.
TEWL is affected by variations in sweat gland activity, temperature, and metabolism.
TEWL becomes a significant factor in dehydration associated with several major disease states.
Water loss through finger and toe nails is called transonychial water loss.
TEWL help in predicting the recurrence of seemingly healed, diabetic, foot ulcers.