Exploring the effects of short-term forest bathing on anxious medical undergraduates’ stressful emotions using near-infrared functional brain imaging and facial expression technology

Background Enrolled medical undergraduates face high exam competition and stress, reducing life quality, well-being, learning abilities and health; supporting their exam stress management is critical. This study used a 2-h forest bathing intervention to alleviate their exam-related stress. Methods One week prior to the intervention, 160 students were recruited via university bulletin boards; eligibility screening, defined by a State–Trait Anxiety Inventory-State score >40, was administered 1 day before the 2-h sensory exposure. Ultimately, 60 final-examination-preparing medical undergraduates (male:female = 7:53) were randomly assigned to two groups ( n = 30 per group). Analyses focused on oxygenated hemoglobin (oxy-Hb) levels in the prefrontal cortex (PFC), physiological functions, and psychological changes under specific tasks. Results Forest environments characterized by lower noise levels, and higher negative air ion concentrations—with a comfort index of 0.971–1.368 (vs. 2.221–3.647 in urban areas) and negative oxygen ion concentrations of 1,000–1,200 ions/cm 3 (vs. 400–500 ions/cm 3 in urban areas). For the PFC region, forest group had significantly greater oxy-Hb reduction during the Trier Social Stress Test (TSST) [ t (29) = 3.038, p = 0.005]. At the channel-specific level, forest group had decreased oxy-Hb in the left PFC and bilateral Frontopolar Area during the TSST, while the urban group exhibited increased oxy-Hb in the right PFC during the MT. No between-group oxy-Hb differences were observed in the Stroop task or rumination task. Forest group showed lower heart rate [ F (1,57) = 4.227, p = 0.044], salivary cortisol [ F (1,57) = 4.590, p = 0.036], higher Nature Connection Scale [ F (1,57) = 4.822, p = 0.032], Digit Span Backward Test [ F (1,57) = 6.164, p = 0.016], Montreal Cognitive Assessment scores [ F (1,57) = 12.040, p < 0.001], lower Rumination-Reflection Questionnaire [ F (1,57) = 11.318, p = 0.001]/Perceived Stress Scale scores [ F (1,57) = 6.076, p = 0.017], 56.7% positive facial expressions ( U = 263.000, n = 60, p = 0.002), and elevated positive affect [Profile of Mood States: F (1,57) = 17.063, p < 0.001]. Conclusion Short-term forest bathing reduces physiological stress markers, enhances nature connectedness/positive emotions, alleviates stress via modified cerebral blood flow, and improves memory and reduce cognitive fatigue to a certain extent. As a low-cost, easy-to-implement strategy, it is may recommended for enrolled medical undergraduates’ mental health curricula to build sustainable stress management.