Shinrin-YokuExploring the Health Benefits of Forest Bathing Research

Bum Jin Park, Yuko Tsunetsugu, Tamami Kasetani, Takahide Kagawa, Yoshifumi Miyazaki; Margaret Hansen, Reo Jones, Kirsten Tocchini•Sources (2):The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across JapanShinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review
HighlightsExpertalloy voice
Park, Tsunetsugu, and colleagues conducted a tight crossover design across twenty-four Japanese forest-city pairs, involving two hundred eighty healthy male university students. Each student spent one day in a forest and one day in a city. The exposures were brief, with fourteen minutes of viewing and sixteen minutes of walking. What they measured across both conditions reveals a lot about what forest environments actually do to the body. Salivary cortisol dropped thirteen point four percent after forest viewing and fifteen point eight percent after walking. Pulse rate fell roughly four to six percent. Systolic and diastolic blood pressure each decreased by about two percent. Those numbers capture simultaneous modulation of both the sympatho-adrenal-medullary axis and the hypothalamic-pituitary-adrenal axis, which are the two main stress pathways. The autonomic data are even more striking. High-frequency heart rate variability power, which is the parasympathetic index, rose fifty-six percent after viewing and one hundred two percent after walking in the forest compared to the city. The low-frequency to high-frequency ratio, known as the sympathetic balance index, fell around nineteen percent. The Profile of Mood States scores reflected these changes: forest subjects showed reduced tension, depression, anger, fatigue, and confusion, along with increased vigor. City subjects experienced the opposite trend on nearly every subscale. That's the controlled experiment. The review by Hansen, Jones, and Tocchini then examines what occurs when the question is taken into clinical populations and psychological endpoints. The findings become messier but arguably more meaningful. Morita and colleagues studied four hundred ninety-eight Japanese adults with stress and found that those carrying the highest chronic stress burden experienced the largest reductions in hostility, depression, and anxiety from spending time in the forest. Kim and colleagues provided cognitive behavioral therapy in a forest setting to sixty-three adults with major depressive disorder. The remission rate in the forest group, defined as a Hamilton Rating Scale for Depression score of seven or below, was sixty-one percent, compared to twenty-one percent in the hospital group and five percent in controls. McCaffrey's garden-walking program for forty older adults with depression reduced mean Geriatric Depression Scale scores from thirteen down to nine point four over twelve sessions. The review also traces mechanistic pathways through sensory channels. Igarashi and colleagues used near-infrared spectroscopy to demonstrate that viewing a real plant versus a pictured one produced measurably different prefrontal hemoglobin signals. Real flowers versus silk flowers resulted in stronger autonomic relaxation as indicated by the low-frequency to high-frequency ratio of heart rate variability. Li and colleagues observed increased natural killer cell activity and anti-cancer protein expression after forest bathing. The connection between specific forest compounds and immune outcomes is noted but not yet causally established based on what these papers report directly. Both papers share the same critical limitation: the field experiments involved young, healthy, Japanese men in short exposures, and most reviewed studies examined samples below twenty. Longitudinal data is sparse, and Western population data is nearly absent. Hansen and colleagues explicitly highlight publication bias, noting that the literature skews positive. What the evidence does support across both papers is reliable short-term physiological relaxation and mood improvement from forest exposure. This provides a foundation for forest medicine as a preventive strategy. Making it clinical requires randomized trials, longer follow-up, and populations beyond young Japanese university men.

Park, Tsunetsugu, and colleagues conducted a tight crossover design across twenty-four Japanese forest-city pairs, involving two hundred eighty healthy male university students. Each student spent one day in a forest and one day in a city. The exposures were brief, with fourteen minutes of viewing and sixteen minutes of walking.

What they measured across both conditions reveals a lot about what forest environments actually do to the body.

Salivary cortisol dropped thirteen point four percent after forest viewing and fifteen point eight percent after walking. Pulse rate fell roughly four to six percent. Systolic and diastolic blood pressure each decreased by about two percent.

Those numbers capture simultaneous modulation of both the sympatho-adrenal-medullary axis and the hypothalamic-pituitary-adrenal axis, which are the two main stress pathways. The autonomic data are even more striking. High-frequency heart rate variability power, which is the parasympathetic index, rose fifty-six percent after viewing and one hundred two percent after walking in the forest compared to the city.

The low-frequency to high-frequency ratio, known as the sympathetic balance index, fell around nineteen percent. The Profile of Mood States scores reflected these changes: forest subjects showed reduced tension, depression, anger, fatigue, and confusion, along with increased vigor. City subjects experienced the opposite trend on nearly every subscale.

That's the controlled experiment. The review by Hansen, Jones, and Tocchini then examines what occurs when the question is taken into clinical populations and psychological endpoints. The findings become messier but arguably more meaningful.

Morita and colleagues studied four hundred ninety-eight Japanese adults with stress and found that those carrying the highest chronic stress burden experienced the largest reductions in hostility, depression, and anxiety from spending time in the forest. Kim and colleagues provided cognitive behavioral therapy in a forest setting to sixty-three adults with major depressive disorder. The remission rate in the forest group, defined as a Hamilton Rating Scale for Depression score of seven or below, was sixty-one percent, compared to twenty-one percent in the hospital group and five percent in controls.

McCaffrey's garden-walking program for forty older adults with depression reduced mean Geriatric Depression Scale scores from thirteen down to nine point four over twelve sessions.

The review also traces mechanistic pathways through sensory channels. Igarashi and colleagues used near-infrared spectroscopy to demonstrate that viewing a real plant versus a pictured one produced measurably different prefrontal hemoglobin signals. Real flowers versus silk flowers resulted in stronger autonomic relaxation as indicated by the low-frequency to high-frequency ratio of heart rate variability.

Li and colleagues observed increased natural killer cell activity and anti-cancer protein expression after forest bathing. The connection between specific forest compounds and immune outcomes is noted but not yet causally established based on what these papers report directly.

Both papers share the same critical limitation: the field experiments involved young, healthy, Japanese men in short exposures, and most reviewed studies examined samples below twenty. Longitudinal data is sparse, and Western population data is nearly absent. Hansen and colleagues explicitly highlight publication bias, noting that the literature skews positive.

What the evidence does support across both papers is reliable short-term physiological relaxation and mood improvement from forest exposure. This provides a foundation for forest medicine as a preventive strategy. Making it clinical requires randomized trials, longer follow-up, and populations beyond young Japanese university men.