Measurement and understanding of TEWL

Through this barrier water constantly evaporates from the skin surface, which is reflected in the transepidermal water loss (TEWL). Its full functionality is a basic condition of healthy skin. The measurement of the transepidermal water loss is therefore the most important non-invasive method to characterise the barrier function of the epidermis in both biological and physiological aspects.1

A low TEWL is a characteristic feature for an intact and healthy skin state. As soon as the barrier function of the skin is disrupted even to a very small amount, which is not at all visible to the human eye, the transepidermal water loss (TEWL) is immediately increased. There are also other skin barrier characteristics such as the stratum corneum hydration, the sebum content, the pH value at the skin surface that can offer additional information on the functions of the skin. In general, the stratum corneum moisture content and the TEWL are reverse proportional in healthy skin. However in numerous skin conditions and on specific skin sites this may not be the case, so that a TEWL measurement does not replace the measurement of hydration in the stratum corneum.2

In cosmetic products, different ingredients and galenic concepts are used to increase the effectiveness, often including penetration enhancers to get the active ingredients deeper into the skin. It is however necessary to ensure that there is no negative influence of such compounds on the skin barrier.3 For this reason, TEWL measurements are the key parameter in product safety assessments.