Transepidermal water loss in healthy adults: a systematic review and meta-analysis update.

BACKGROUND: Transepidermal water loss (TEWL) is one of the most important skin barrier characteristics. Higher TEWL is usually associated with skin barrier impairments, and lower TEWL with healthy skin. OBJECTIVES: To update an existing systematic review and meta-analysis to provide TEWL reference values for healthy skin in adults. METHODS: The databases MEDLINE and Embase and other sources were searched. This update includes studies identified by two combined searches that cover the period from 1947 to 13 April 2017. Primary empirical observational and interventional studies in healthy adults providing quantitative estimates of TEWL measurements including measures of spread, such as SDs, with clear reporting of skin areas and age were included. Data were extracted per skin area and statistically pooled. RESULTS: After full-text assessment, the results of 45 studies were included additionally to the existing meta-analysis. TEWL estimates were identified for 86 skin areas in 212 studies. The lowest TEWL of 2·3 g m-2 h-1 (95% confidence interval 1·9-2·7) was reported for breast skin and the highest TEWL of 44·0 g m-2 h-1 (95% confidence interval 39·8-48·2) for the axilla. Sample sizes ranged from four (forehead middle left middle) to 4013 (mid volar right forearm). The clinical relevance of the difference between TEWL estimates for different measurement devices seems to be minimal. TEWL in elderly patients was either similar to or lower than values in the younger group. CONCLUSIONS: Reference estimates are useful for clinical study planning and interpretation of results. TEWL is highly dependent on skin area, and our results further support the symmetry between right and left measuring sites. TEWL in elderly people seems to be generally similar or decreased compared with younger individuals, but available evidence is limited. Reporting of TEWL should be improved: mean and spread parameters should always be reported in future studies.