Transepidermal water loss (TEWL) is one of the most important objective measurements in dermatology clinical research. If you are participating in an eczema trial, you may hear this term frequently.
What Is TEWL?
TEWL measures how much water evaporates through the skin’s outer layer (the stratum corneum). A healthy skin barrier keeps moisture inside the body. In eczema, the barrier is compromised, allowing excessive water to escape.
Why Does TEWL Matter for Eczema?
High TEWL indicates a damaged skin barrier, which is both a cause and a consequence of eczema inflammation. When the barrier is weak, environmental irritants, allergens, and bacteria can more easily penetrate the skin, triggering immune reactions.
Measuring TEWL at baseline and throughout a clinical trial gives researchers an objective way to track whether a treatment is improving barrier function, independent of physician or patient-reported scores.
How Is TEWL Measured?
TEWL is measured with a Tewameter, a small probe held against the skin for 15 to 30 seconds. The device measures the water vapor concentration gradient at the skin surface. It is painless and takes only minutes.
What Is a Normal TEWL?
On healthy skin, TEWL is typically below 10 g/m2/h. On eczema-affected skin, TEWL can be significantly elevated, sometimes exceeding 30 g/m2/h.
TEWL at NuLine
NuLine uses a Courage + Khazaka Tewameter as part of our dermatology trial assessments. This objective data complements physician-scored tools like EASI and supports more rigorous trial outcomes.
Learn more about our eczema studies.