Skin hydration outperforms other measures in predicting age-related skin barrier changes and systemic inflammation

Summary: Abstract Body: Age-related skin barrier decline may contribute to systemic inflammation; however, the best measures of skin barrier function to capture these changes remain unclear. In this cross-sectional study, we compared skin barrier function between young and older adults at the dorsal forearm and upper buttock. Skin barrier function was assessed via transepidermal water loss (TEWL), stratum corneum hydration (SCH), and skin pH. TEWL measurement was repeated after tape stripping in increments of 5 tape strips. The area under the curve (AUC) and slope were calculated from scatter plots of TEWL values against the number of tape strips. Serum inflammatory markers were measured using a 25-plex Luminex assay, and a composite z-score was averaged from standardized z-scores of 9 detectable markers. Thirty healthy participants were included, with 16 young adults (mean age 25.9, SD 3.5 years) and 14 older adults (mean age 79.1, SD 6.8 years). The older adult group showed mixed results regarding skin barrier function. At the forearm, worse barrier function was indicated by lower SCH (unadjusted p=0.021; adjusted p=0.007 for sex, BMI, baseline TEWL, and pH) and a significantly higher baseline TEWL/SCH ratio (unadjusted p=0.026; adjusted p=0.228 for sex and BMI). Baseline TEWL, TEWL AUC, slope, and pH did not differ between the young and older adult groups. At the upper buttock, no significant differences were observed for any measure. Additionally, all participants were divided into two groups based on z-scores, with higher z-scores assumed to indicate higher inflammatory status. At the forearm, participants with higher z-scores exhibited lower SCH (unadjusted p=0.028; adjusted p=0.454 for age, sex, BMI, baseline TEWL, and pH), suggesting worse skin barrier function. However, no significant differences were observed in baseline TEWL, TEWL AUC, baseline TEWL/SCH ratio, slope, or pH. At the upper buttock, no significant differences were found between the lower and higher z-score groups across any measures. Jie Zhu¹, Richard Kim¹, Emma Doan¹, Benjamin Stroebel¹, Katrina Abuabara¹ 1. Department of Dermatology, University of California San Francisco, San Francisco, CA, United States. Epidermal Structure and Barrier Function