Tewameter

The tewameter is a scientific instrument used to measure transepidermal water loss (TEWL), an indicator of the skin’s barrier function. TEWL quantifies the rate at which water vapor passes from the skin into the surrounding environment, reflecting the integrity of the epidermal barrier.

Principle of operation and design: A tewameter places a small probe on the skin surface, enclosing a miniature measurement chamber. Humidity and sometimes temperature sensors inside the chamber monitor the water vapor gradient created by evaporation from the skin. From the measured vapor pressure gradient and the chamber’s geometry, the device calculates TEWL, typically expressed in grams per square meter per hour (g/m^2/h). There are open-chamber designs, which allow air exchange with the surrounding environment, and less common closed-chamber variants, each with specific advantages for certain studies.

Applications: Tewameters are widely used in dermatology and cosmetic science to assess skin barrier function, monitor wound healing, and evaluate the efficacy of moisturizers, cleansers, and other topical formulations. They are employed in clinical research, product development, and regulatory-supported testing to compare treatments, formulations, or skin conditions such as atopic dermatitis and psoriasis.

Procedure and limitations: Measurements are typically conducted in a controlled environment with stable temperature and humidity. The probe is applied to clean, prepared skin and measurements are repeated to obtain an average TEWL value. TEWL readings are influenced by environmental conditions, skin site, hydration, and air flow, so careful experimental standardization is essential. TEWL is a component of skin health and is interpreted alongside other clinical or biochemical markers.