Choosing the Right Tewl Device: A Comparison of Inter‐ and Intra‐Device Reliability of the Vapometer and Dermalab across Measurement Ranges

BACKGROUND: Measurement of transepidermal water loss (TEWL) is widely used to evaluate skin barrier function. MATERIALS AND METHODS: This study compared two devices-the DermaLab (DL) TEWL probe and the VapoMeter (VM) - from data collected across three studies to measure TEWL in scarred and normal skin. Each site was measured three times per device, alternating devices to allow vapor clearance. Inter-device reliability was assessed from 1,617 paired locations, each averaged from the three readings. Intra-observer reliability was able to be determined from a dataset of 1,628 DL and 1,635 VM measurements. RESULTS: Data were stratified into low, medium, and high TEWL ranges based on measurement distribution and observations. Overall inter-device reliability was 'good' but varied by range: 'poor' in low, 'excellent' in medium, and 'moderate' in high TEWL ranges. In the medium range, the VM reported nearly twice the TEWL values compared to the DL, while in the high range, it read approximately 34% higher. CONCLUSIONS: Both devices showed excellent intra-observer reliability overall. However, in the low TEWL range, the DL exhibited 'moderate' reliability, whereas the VM showed slightly better, 'good' reliability. Differences in chamber architecture-semiopen for the DermaLab and closed for the VM-appear to drive the observed variability in measurement reliability across TEWL ranges. Analysis of this large dataset indicates that the VM likely approaches saturation at the categorized 'high' TEWL values, constraining its accuracy, whereas the DermaLab exhibits reduced measurement stability at low TEWL levels, limiting its applicability under those conditions. Targeted methodological work is needed to refine DL performance in the lowTEWL regime and to more precisely define the upper operational limit of the VM.