Transepidermal water loss in young and aged healthy humans: a systematic review and meta-analysis.

Transepidermal water loss (TEWL) is regarded as one of the most important parameters for characterizing skin barrier function but an agreed upon definition of what a "normal" TEWL is does not exist. In order to determine generalizable TEWL values for healthy adults, a systematic review and meta-analysis was conducted. The databases MEDLINE and EMBASE and publication lists were screened. After full-text appraisal of 398 studies, 231 studies were excluded due to unclear or insufficient reporting. 167 studies providing data about 50 skin areas were included in the final data synthesis. Pooled sample sizes ranged from n = 5 for the left cheek and the left lower back to a maximum of n = 2,838 for the right midvolar forearm area. The lowest TEWL of 2.3 (95 % CI 1.9-2.7) g/m(2)/h was calculated for the breast skin, the highest TEWL of 44.0 (39.8-48.2) g/m(2)/h for the axilla. TEWL in individuals being 65 years and above was consistently lower compared to the group of 18- to 64-year-old individuals. The quality of reporting TEWL in humans should be increased in future studies.