Forest Bathing and Cortisol: Does Time in the Woods Actually Lower Stress Hormones?

Forest bathing, or shinrin-yoku, originated in Japan in the 1980s as a public health concept, coined by Japan's forestry agency to encourage people to spend unhurried, sensory-focused time among trees. It is deliberately not a workout: the practice is slow walking, sitting, and paying attention to sound, smell, and light in a forest setting, rather than covering distance. In recent years it has been folded into "cortisol face" and stress-skin content as a natural remedy, which raises a fair question: is there real evidence this specific practice changes stress hormone levels, or is it riding on the general, well-known benefits of being outdoors?

Forest bathing actually has one of the more substantial evidence bases among nature-based wellness trends. A 2019 systematic review and meta-analysis in the International Journal of Biometeorology screened 971 studies, ultimately including 22 in the systematic review and 8 in the meta-analysis. Pooling that data, the review found salivary cortisol was significantly lower in forest groups compared with urban control groups, both before and after the intervention sessions, with the post-intervention difference amounting to roughly 0.05 micrograms per deciliter. In all but two of the included studies, cortisol was either lower after a forest session compared to a control condition, or dropped significantly from pre- to post-session within the forest group itself.

The proposed mechanisms are still being worked out. Some researchers point to phytoncides, airborne organic compounds released by trees, which earlier laboratory work has associated with increased natural killer cell activity, part of the immune system rather than the stress-hormone system directly. Others emphasize simpler explanations: forests reduce traffic noise, artificial light, and the general sensory load of urban environments, which plausibly shifts the body toward parasympathetic, "rest and digest" activity. The current research does not clearly isolate which of these factors, if any single one, is doing the work.

Research in this area has also started moving beyond cortisol specifically. A 2025 randomized crossover study in the journal Diseases, led by longtime shinrin-yoku researcher Qing Li, had 31 women with depression or depressive tendencies alternate forest walks and city walks, measuring blood serotonin, oxytocin, IGF-1, and standardized depression and mood questionnaires rather than cortisol. The forest condition was associated with reduced depression scores and improved mood ratings compared to the city walk, with effects reported to persist a week later. That is a genuinely interesting result, but it speaks to mood biomarkers, not a direct cortisol measurement, and the sample size was small.

The authors of the 2019 meta-analysis were notably careful about their own findings, explicitly noting that "anticipated placebo effects" could be playing a meaningful role in the cortisol reductions they found, and calling for more rigorous research given the limited quality of data available across the studies pooled. That caveat is worth taking seriously: proven, here, means a real, statistically documented association between forest exposure and lower salivary cortisol across multiple small trials, not a confirmed, mechanism-clear treatment. Not proven is the idea, common in "cortisol face" marketing, that forest bathing "detoxes" cortisol or that it meaningfully outperforms other unhurried outdoor time.

None of this requires an actual old-growth forest to be worth trying. Given the low cost and low risk, an unhurried walk of 20 to 90 minutes in whatever green space is accessible, ideally without a phone, is a reasonable evidence-informed way to spend time, and it lines up with broader, well-established research on nature exposure and stress. Just don't expect it, on its own, to reverse a skin or hormone symptom that has a different underlying cause.