Regional variability in skin water and heat loss during hemodialysis indicates site-specific skin barrier regulation

Background: While the kidney is established as key organ for water and electrolyte homeostasis, emerging evidence highlights the skin as crucial regulator of whole-body water balance. We hence hypothesized that acute fluid removal during hemodialysis (HD) impacts skin barrier function, assessed by measurements of transepidermal water loss (TEWL) and heat loss. Methods: In our prospective, monocentric SkInDialysis study, 11 maintenance HD patients (27% female, mean age 55.4 ± 13.3 years) underwent measurements of TEWL, skin hydration, temperature and heat loss at three sites (forearm, face, trunk) before, during (+20, +80, +160 min), and directly after HD. Measurements were performed under climate-controlled conditions using a Tewameter and a Corneometer. Results: Baseline TEWL was significantly higher at the face (13.9 ± 5.5 mL/h/m²) than at forearm (8.5 ± 3.0 mL/h/m², p = 0.001) and trunk (8.9 ± 3.1 mL/h/m², p = 0.001). During HD, forearm TEWL decreased within 20 min (p = 0.002), consistent with vasoconstriction, then returned to baseline by session end. In contrast, facial TEWL rose early (p = 0.01) and remained elevated; trunk TEWL was unchanged (p = 0.75). Evaporative cooling correlated strongly (R > 0.9) with TEWL, whereas correlations with heat diffusion were moderate (R = 0.40–0.52), suggesting distinct physiological processes. Conclusion: HD induces rapid, site-specific alterations in skin water loss and heat diffusion, reflecting heterogeneous microcirculatory and barrier responses. This is the first study quantifying TEWL at multiple skin sites during HD, emphasizing the emerging role of the skin as fast responder to body fluid alterations.