Effects of repeated balneotherapy on skin hydration and psychophysiological stress: findings from a 16-week korean spa trial

Balneotherapy has traditionally been associated with skin health and psychological well-being. However, few studies have assessed its effects during extended use in real-world, community-based settings. This study aimed to evaluate the effects of repeated balneotherapy on skin barrier function and psychological stress regulation in middle-aged women. A 16-week quasi-experimental trial was conducted in Asan, Republic of Korea, involving 58 community-dwelling women aged 40-64 years. Participants were assigned to either an intervention group (n = 29), which received biweekly 20-minute immersion sessions in naturally mineralized hot spring water, or a control group (n = 29) with no spa exposure. Primary outcomes included corneometry-based skin hydration and transepidermal water loss (TEWL). Secondary outcomes were assessed using the Stress Response Inventory (SRI), salivary cortisol, heart rate variability (HRV), and the Patient Global Impression of Change (PGIC). Significant in-group improvements were observed in the intervention group for skin hydration (p < 0.001), TEWL (p < 0.001), and SRI scores (p = 0.043). Between-group comparisons at week 16 showed significant differences for skin hydration, TEWL, SRI, and PGIC (all p < 0.05), whereas no significant differences were found for salivary cortisol or HRV. Repeated balneotherapy over 16 weeks improved skin barrier function and reduced psychological stress in middle-aged women. These findings support the feasibility of thermal bathing as a non-pharmacologic, community-based intervention for preventive wellness and highlight the need for larger randomized trials with long-term follow-up.