EEMCO guidance for the assessment of transepidermal water loss in cosmetic sciences

Measurement of transepidermal water loss (TEWL), based on the estimation of the water vapour gradient in an open chamber, is being used to support claims of cosmetics including product mildness, reduction in irritative skin reactions, skin hydration, skin repair, protective effect against UV damage and others. TEWL measurement can also screen ingredients that have a beneficial effect on the barrier function and offer the possibility to monitor in vivo, on human skin, the effect of topical treatment in an objective and non-invasive way. A high number of variables affecting TEWL measurements have been identified. These should be rigorously taken into consideration. To work under standardised conditions is of the utmost importance to obtain reliable and reproducible results.