Forest Bathing (Shinrin-Yoku)

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1. What Forest Bathing Is

Forest bathing (Japanese Shinrin-yoku) denotes conscious time spent in forest areas with the aim of promoting mental and physical health. Developed in Japan in the 1980s, it comprises no specific exercises but rather the mindful perception of the surroundings – for example through walking, sitting or perception exercises. Duration varies; stays of several hours are typical. In contrast to sport or recreation outdoors, the emphasis is not on physical activity but on sensory exposure to the forest atmosphere, including volatile organic compounds (phytoncides), odours and visual stimuli.

The execution is not standardised: studies use different forest types (deciduous, coniferous, mixed forests), seasons, times of day and accompanying activities (e.g. meditation, breathing exercises). Mainly subjective parameters such as mood or stress perception as well as physiological markers such as heart-rate variability, cortisol level or immune parameters are measured. As no chemical substance or defined dose is present, the comparability of studies depends strongly on the description of the intervention. Many studies forgo a detailed characterisation of the forest environment, which restricts reproducibility.

2. What the Studies Show in Detail

The supporting human studies and the most important reviews — by application area, with population, duration, preparation, measured variable and result, as the original studies report them. Numbers appear only where the study states them.

Distribution of the controlled human studies by application area — the numbers are not additive, as one study may be assigned to several areas:

Inflammatory Processes

In a randomised controlled study (RCT) with 24 older patients (mean age not explicitly stated) with essential hypertension, the effect of a 7-day forest stay (“forest bathing”) on inflammation-relevant biomarkers was examined. The intervention group spent 7 days and nights in an evergreen deciduous forest, while the control group remained in an urban environment in Hangzhou. Measured, among other things, were the inflammatory markers interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α), as well as cardiovascular risk factors such as endothelin-1, homocysteine, renin, angiotensinogen, angiotensin II and its receptors. The results showed a significant reduction in blood-pressure values as well as the inflammatory markers IL-6 and TNF-α in the forest group compared with the control group. The study was, however, subject to limitations such as a small sample and the lack of blinding, which restricts the strength of the statements.

A systematic review from 2017 analysed six RCTs on the health effects of nature interventions, including studies on the effect of forest therapy on inflammatory markers 1. The work comprised various forms of nature intervention, including forest bathing. Three of the six studies reported positive effects on inflammation parameters, whereby the methodological quality of all included studies was rated as high risk of bias (“high risk of bias”). This restricts the generalisability of the results. In addition, detailed information on the specific inflammatory markers and their quantitative changes was lacking.

Hypothesis The available data provide indications that forest bathing could influence inflammatory markers, particularly in individuals with pre-existing cardiovascular risk factors. However, large-scale, longitudinal studies with standardised measurement methods are still pending to investigate these changes and possible dose-response relationships.

Heart and Circulation

A systematic review and meta-analysis from 2017 examined the blood pressure-lowering effect of Shinrin-yoku (forest bathing) based on 20 studies with a total of 732 participants 2. The included controlled and comparative studies analysed the effect of forest environments on systolic and diastolic blood pressure. The meta-analysis found that both systolic and diastolic blood pressure were significantly lower in the forest environment than in non-natural environments. Effect sizes were not explicitly quantified; the clinical relevance of the blood pressure reduction therefore remains open. Limitations of the analysis included heterogeneity of the study populations, varying intervention durations (from single visits to multi-week programmes) and the lack of standardisation of forest environments.

The participants were divided into two groups: one group completed a forest therapy programme (n = 23) and the other a mountain hiking programme (n = 22). Both interventions extended over an unspecified period and, in this comparative observational study, led to small changes in blood pressure in both groups. Women additionally showed changes in physiological parameters such as increased aerobic capacity and an increase in skeletal muscle mass. However, the study was limited by a small sample size and the absence of a non-intervention control group or randomisation, which restricts the strength of the findings.

A further RCT from 2022 examined the combined effect of a Mediterranean DASH diet (MIND diet) and forest bathing on older Chinese adults with hypertension (n = 72) 8. The participants were assigned to three groups: MIND diet alone (n = 23), MIND diet combined with forest bathing (n = 25) and a control group (n = 24). After four weeks of intervention, both intervention groups showed a significant reduction in systolic blood pressure, while the combined group additionally showed a significant reduction in anxiety and negative mood states. The study provides an indication of effects of the combined intervention but does not permit conclusions about the specific effect of forest bathing alone. It was also limited by the short intervention duration and the lack of follow-up measurement, so long-term effects remain unclear.

Hypothesis The available studies suggest that forest bathing could represent a promising non-pharmacological intervention for blood pressure reduction, particularly in combination with other health-promoting measures. However, systematic investigation of the optimal duration, frequency and type of forest environment is still pending to derive clear recommendations for clinical practice.

Cognition and Psyche

An RCT from 2020 examined the efficacy of a multimodal therapy programme for fibromyalgia patients (NAT-FM), which included forest bathing as one component 3. A total of 169 participants were randomised to either the intervention group (TAU + NAT-FM) or the control group (TAU alone). The 12-week programme comprised pain neuroeducation, exercise therapy, cognitive behavioural therapy, mindfulness and nature activities such as yoga, Nordic walking, nature photography and Shinrin-yoku. The primary endpoint was change in functional impairment (FIQR); secondary endpoints included pain, fatigue, anxiety, depression, physical functioning and stress. The results showed significant improvements in the intervention group regarding functional impairment, pain, fatigue and mental health. However, the study was limited by the absence of an active control group and the combination of multiple interventions, so the specific contribution of forest bathing could not be isolated.

A meta-analysis from 2022 analysed six RCTs on the effect of forest-based interventions on mental health, including anxiety, depression and positive and negative mood states 9. The included studies comprised a total of 34 outcome variables. The pooled effect size of the forest therapy programmes was 1.25 (95 % CI = 0.93–1.57, p < 0.001), indicating a large and statistically significant effect. However, the studies were characterised by high heterogeneity with regard to populations, intervention duration and measurement instruments. In addition, detailed information on the specific mechanisms underlying the observed effects was lacking.

The participants were surveyed on a forest day and a control day, with mood assessed using the Multiple Mood Scale-Short Form and the State-Trait Anxiety Inventory A-State Scale. The results showed a significant reduction in hostility (p < 0.001) and depression (p < 0.001) as well as an increase in vigour (p = 0.001) on the forest day compared with the control day. However, the study was limited by the absence of randomisation and an active control group, so selection effects cannot be ruled out.

Hypothesis Individual studies suggest that forest bathing could have positive effects on cognitive function and mental health, particularly in individuals with pre-existing mental stress. Long-term effects and neurobiological mechanisms are still pending.

Immune System

A systematic review from 2021 analysed 13 studies on the effect of forest therapy on immunological laboratory parameters in adults 5. The included studies comprised RCTs, non-randomised controlled studies and pre-post studies without a control group. The interventions were divided into two categories: overnight programmes (“lodging-type”) and session programmes (“session-type”). Primary outcome measures were the number of natural killer cells (NK cells), their cytotoxic activity and the expression of cytotoxic effector molecules such as granulysin, perforin and granzyme A/B. Most studies reported an improvement in these parameters after the intervention compared with baseline values. However, the studies were limited by small samples, lack of control groups and high heterogeneity with regard to intervention duration and intensity.

A review from 2010 examined the effect of forest bathing on immunological laboratory parameters based on several studies with Japanese adults 20. The participants completed a 3-day/2-night forest therapy programme, with blood and urine samples taken on days 2, 3, 7 and 30 after the intervention. The results showed a significant increase in NK-cell activity as well as in the number of NK cells and lymphocytes expressing granulysin, perforin and granzyme A/B. At the same time, the concentration of adrenaline in urine decreased. The increased NK-cell activity persisted for 30 days after the intervention. However, the study was limited by the absence of a control group, the small sample size and the restriction to laboratory findings, so the clinical relevance of these changes in humans has not been investigated.

Hypothesis The available data provide indications that forest bathing could positively influence NK-cell activity as a preclinical immune parameter. Whether this results in a clinically relevant immune effect is still pending. Large-scale, randomised controlled studies with standardised immune parameters are required to examine these effects.

Fatigue and Stress

An observational study from 2011 examined the physiological and psychological effects of forest bathing in 12 young Japanese men 19. The participants spent one day in a forest area, with salivary cortisol, pulse rate and heart rate variability (HRV) measured before and after the intervention. The results showed a significant increase in parasympathetic activity and a decrease in sympathetic activity in the forest compared with an urban environment. In addition, cortisol levels and pulse rate decreased significantly. Psychological tests showed an increase in positive mood states and a decrease in negative moods. However, the study was limited by a small, homogeneous sample and the absence of a control group.

A meta-analysis and systematic review from 2024 compared the stress-reducing effects of digital nature (e.g. 360° videos) with real nature, including some studies on forest bathing 11. The work included ten studies with a total of 886 participants on various nature interventions. The results showed that digital nature environments had a similar stress-reducing effect to real nature (SMD = -0.01; 95 % CI: -0.15, 0.12). Subgroup analyses on forest bathing found no significant differences between subjective and physiological stress measures. However, the study was limited by the heterogeneity of the interventions and measurement instruments, so the results must be interpreted with caution.

The participants were randomised to either a 3-hour guided session of a related but independent procedure (forest therapy) or a control group (free day without clinical duties). The results of this study on forest therapy showed no significant differences in burnout symptoms between the groups, which may be due to the short intervention duration and the small sample size. Transferability to forest bathing has not been investigated.

Hypothesis The available data suggest that forest bathing could have stress-reducing effects, particularly through modulation of the autonomic nervous system.

Overall Picture

Some of the available controlled studies suggest that forest bathing (Shinrin-yoku) could have positive effects on various physiological and psychological health parameters. Individual controlled studies showed results in the areas of blood pressure reduction, stress reduction and improvement in mental health. The effects on inflammatory markers, cognitive function and fatigue are promising but still pending. Many studies, including observational studies, have methodological limitations such as small samples, lack of control groups, short intervention durations and high heterogeneity with regard to the type of forest environment and the measured outcomes.

A central deficit of the current research situation is the lack of large-scale, longitudinal studies with standardised measurement methods. In addition, there is a lack of studies that systematically investigate the underlying mechanisms of the observed effects, particularly with regard to neurobiological and immunological processes. The question of which specific components of the forest environment (e.g. vegetation type, air quality, sounds) are responsible for the health effects also remains largely unresolved.

3. How Robust the Research Is

Research focuses on two application areas: fatigue and cognition. Cardiovascular parameters, metabolism or the immune system are examined far less often. Most controlled studies date from the last ten years. Systematic reviews – which often encompass many modalities such as urban green spaces or general nature contact – complement the field, while observational studies frequently show associations between nature contact and well-being without specifically demonstrating causal effects for forest bathing.

The methodological quality of the controlled studies varies widely. Many works have small sample sizes, and only a few use blinded designs – which is hardly feasible with an intervention such as forest bathing. Active control groups (e.g. city walks) are frequently absent, so placebo effects or expectation biases cannot be ruled out. The most-cited review articles (e.g. on urban green spaces or immune function) often cover many modalities and are based on observational data without specifically demonstrating causal effects for forest bathing. Laboratory studies on mechanisms (e.g. phytoncides) remain largely theoretical, as they are not directly transferable to application in the forest.

4. What Is Frequently Claimed — and What the Data Support

5. The Most Robust Studies

Ordered by strength of evidence, not by prominence. The complete evaluation comprises considerably more studies; the most robust ones are listed here.

Controlled Human Studies

• 1 Health and well-being benefits of spending time in forests: systematic review (2017)
• 2 Blood pressure-lowering effect of Shinrin-yoku (Forest bathing): a systematic review and meta-analysis (2017)
• 3 Effectiveness of a Multicomponent Treatment for Fibromyalgia Based on Pain Neuroscience Education, Exercise Therapy, Psychological Support, and Nature (2020)
• 4 The effect of nature exposure on the mental health of patients: a systematic review (2019)
• 5 The Effects of Forest Therapy on Immune Function (2021)
• 6 The Effects of Nature Exposure Therapies on Stress, Depression, and Anxiety Levels: A Systematic Review (2024)
• 7 Assessing the Impact of a Shinrin-Yoku (Forest Bathing) Intervention on Physician/Healthcare Professional Burnout: A Randomized, Controlled Trial (2022)
• 8 Cardiac and Mental Benefits of Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) Diet plus Forest Bathing (FB) versus MIND Diet among (2022)
• 9 Effects of Forest-Based Interventions on Mental Health: A Meta-Analysis of Randomized Controlled Trials (2022)
• Gender Differences in Impacts of Place-Based Neighborhood Greening Interventions on Fear of Violence Based on a Cluster-Randomized Controlled Trial (2021)
• 10 Long-Term Effects of Mountain Hiking vs. Forest Therapy on Physical and Mental Health of Couples: A Randomized Controlled Trial (2023)
• Efficacy of a Multicomponent Intervention for Fibromyalgia Based on Pain Neuroscience Education, Exercise Therapy, Psychological Support, and Nature E (2020)
• 11 The effects of digital nature and actual nature on stress reduction: A meta-analysis and systematic review (2024)
• 12 Effects of Outdoor Walking on Positive and Negative Affect: Nature Contact Makes a Big Difference (2022)
• Stepped-Wedge Cluster Randomised Trial of Social Prescribing of Forest Therapy for Quality of Life and Biopsychosocial Wellbeing in Community-Living A (2020)
• Mindfulness-based Therapeutic Sailing for Veterans With Psychiatric and Substance Use Disorders (2022)
• 13 A Nature-Based Intervention and Mental Health of Schoolchildren: A Cluster Randomized Clinical Trial (2024)
• 14 Taking real steps in virtual nature: a randomized blinded trial (2022)
• Effects of the school-based integrated health promotion programme with hydroponic cultivation on the use of and satisfaction with green spaces, dietary habits and Ment (2021)
• 15 Enhancing patient well-being in oncology waiting rooms: a pilot field experiment on the emotional impact of virtual forest therapy (2024)
• 16 Randomized controlled trial on the efficacy of forest walking compared to urban walking in enhancing mucosal immunity (2025)
• 17 Effects of a Virtual Reality-Based Natural Environment Intervention on Attention and Mood in Community-Dwelling Older Adults: Randomized Controlled Tr (2026)
• The effect of nature contact on pain experience and quality of life in patients with chronic pain: a systematic review and meta-analysis protocol (2023)
• 18 Physiological adjustment effects of viewing natural environment images on heart rate variability in individuals with depressive and anxiety disorders (2025)

6. Summary

What is shown: Forest bathing demonstrates consistent effects in the present controlled studies on stress parameters (cortisol, heart rate variability), mental health (anxiety, depression, mood) and cardiovascular markers (blood pressure). Immunological parameters such as NK-cell activity and inflammatory markers (IL-6, TNF-α) provide indications of improvements in small, methodologically limited studies. The evidence is strongest for exhaustion, stress and cognition, while other areas such as metabolism or the gut microbiome remain scarcely researched. The controlled studies and observational studies encompass heterogeneous populations and intervention designs, limiting comparability.

Hypothesis The present controlled studies indicate that forest bathing as a non-pharmacological intervention for stress reduction, blood-pressure lowering and mental stabilisation is plausible. Possible mechanisms include modulation of the autonomic nervous system, preclinical indications of immunological effects from cell-culture work and sensory exposure to forest atmosphere. Whether the processes observed in cell cultures also occur in humans remains to be investigated. It could follow that forest bathing might serve as a supportive measure in prevention or rehabilitation, particularly for stress-associated or cardiovascular conditions. However, clear dose-response relationships, standardised protocols and long-term studies are still required before clinical recommendations can be derived.

What a study would need to clarify: Large-scale randomised controlled trials with active control groups (e.g. urban walks) and standardised forest environments would be necessary to establish causal effects. Systematic investigations into optimal duration, frequency and type of forest environment (deciduous, coniferous, mixed) could yield clear practical recommendations. In addition, long-term studies would need to evaluate the persistence of effects and possible clinical applications. Mechanistic studies should elucidate the role of specific forest components (phytoncides, odours, visual stimuli) and their contribution to the observed effects.

7. What Remains Open

• Standardisation: How long, how often and in which forest type should forest bathing be performed to achieve reproducible effects?
• Long-term effects: Do the observed changes (e.g. stress reduction) persist over weeks or months?
• Mechanisms: What role do phytoncides, microclimate or psychological factors play – and how do they interact?