What Is Transepidermal Water Loss?
What It Is
Transepidermal water loss (TEWL) describes the movement of water out through the skin and is used in dermatology as a measurable marker of skin-barrier function.
What It Does
TEWL itself is not a biological ingredient or treatment. It is a measurement used to assess how effectively the skin barrier limits water loss. The source describes higher TEWL as associated with a more compromised barrier.
How It Functions in a Formulation
TEWL is not a formulation ingredient. It is an outcome measure that can be used when studying how bathing, hot water, cleansers, skin conditions or barrier-supporting practices affect skin-barrier behaviour.
Safety and Tolerance
TEWL does not itself create a safety concern. Its relevance is interpretive: changes in TEWL can indicate changes in barrier function, and barrier-compromising practices can be associated with increased water loss.
What the Source Supports
The source supports TEWL as an objective dermatological measure of water loss through the skin and as a useful marker when discussing barrier health and the effects of bathing or topical products.