Rapid Skin Responses to a Low Humidity Environment and the Benefits of a Fine Fiber Film

BACKGROUND: A short single low-humidity stay (SSLHS) induces rapid changes in stratum corneum (SC) function, but their significance and inter-individual variability remain unclear. We examined associations between baseline SC function and rapid SSLHS responses and evaluated whether a lotion-free fine fiber (FF) film modulates these responses. MATERIALS AND METHODS: Forty healthy Japanese women (n = 40) completed 6-h stays at 60% RH and, on the next day, 20% RH (23°C). TEWL, capacitance, and skin texture were measured on the open cheek at 0, 3, and 6 h. During SSLHS, an FF film was applied to the right half of the face and assessed at 0 and 6 h. Pearson's r and within-subject differences in absolute change (absΔ; FF - open) are reported with 95% confidence intervals (95%CI). RESULTS: TEWL decreased under both RH conditions, whereas capacitance increased only at 60% RH. Under SSLHS, absΔTEWL (3 h-0 h) was associated with baseline TEWL (r = 0.661, 95%CI 0.44-0.81), capacitance (r = -0.504, 95%CI -0.70 to -0.23), and SEr (r = 0.518, 95%CI 0.25-0.71). During SSLHS, the FF film reduced absΔTEWL (mean difference -1.22 [95%CI -2.36, -0.09]) and increased absΔCapacitance (+2.20 [0.87, 3.54]) versus the open side. Exploratory subgroup analysis suggested larger differences in subjects classified as sensitive. CONCLUSION: Rapid low-humidity responses vary with baseline SC function, and an FF film without lotion modulates short-term responses to low humidity.