Quantitative evaluation of skin barrier function using water evaporation time related to transepidermal water loss

BACKGROUND: Transepidermal water loss (TEWL) is often used as an index for skin barrier function. The skin barrier tester, SBT‐100 (Rousette Strategy Inc), measures the TEWL, water evaporation time, and time constant by contacting the skin and diffusing water into the closing measurement chamber. However, the relationship between the TEWL and time constant has not been sufficiently investigated. This study involved analyzing the underlying measurement principle and obtaining data through two experiments. MATERIALS AND METHODS: The TEWL and time constant were measured using SBT‐100. Experiment 1 produced a simple simulation model for continuous water evaporation from the skin using a moisture‐permeable film. In experiment 2, four skin sites of 43 healthy volunteers were examined from May to September 2018. RESULTS: In experiment 1, the TEWL increased and time constant decreased, following an increase in humidity in the external environment. Both parameters demonstrated significant negative correlation (drying: ρ = −0.832, p < 0.001). For the 43 healthy volunteers who participated in experiment 2, their TEWL increased and time constant decreased in summer. For all skin measurement sites, both data demonstrated significant negative correlation (forehead: ρ = −0.909, p < 0.001; back of the left hand: ρ = −0.829, p < 0.001; left lateral elbow: ρ = −0.896, p < 0.001; left lateral malleolus: ρ = −0.865, p < 0.001). CONCLUSION: Results indicated that the time constant is significantly correlated with TEWL. Furthermore, the time constant can be used as a parameter for evaluating skin barrier function.