The Tewitro® TW 24R device, developed by Courage + Khazaka, Cologne, has proven its value to reliably measure the transepithelial water loss (TEWL) in 3-dimensional human Phenion® Full-Thickness Skin Models. The TEWL is a meaningful parameter to assess the physiological status of the dermal barrier, which, if intact, protects our skin against environmental impacts and prevents undesired water loss.