Table 5.
Outcomes of human studies. Significances are given with p < 0.05, p < 0.01 and p < 0.001; NS = not significant, NA = not applicable. A non-significant trend is described as “Decrease/Increase, NS”. If significances are not given, it is described as “Decrease/Increase, NA”.
| Outcome | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Main Author |
Year | Title | Measure | Intervention (Compared to Baseline) | p-Value | Control (Compared to Baseline) | p-Value | Comparison (Intervention Compared to Control) | p-Value | Conclusion | Comment | |
| Forest bathing | ||||||||||||
| Han et al. [45] | 2016 | The effects of forest therapy on coping with chronic widespread pain | NK cell activity | Increase | p < 0.001 | NS | Increase | NA | NK cell activity increases after a forest bathing trip in adults with chronic pain. | Significant baseline differences between control and intervention group in NK cell activity. | ||
| Im et al. [44] | 2016 | Comparison of effect of two-hour exposure to forest and urban environments on cytokine, anti-oxidant and stress levels in young adults | IL-6 level in serum | NS | Pro-inflammatory cytokine level (IL-8 and TNFα, but not IL-6) is reduced in healthy students after a forest bathing trip. | No pre-intervention data shown. | ||||||
| IL-8 level in serum | Decrease | p < 0.001 | ||||||||||
| TNFα level in serum | Decrease | p < 0.001 | ||||||||||
| Glutathione peroxidase (GPx) level in serum | Increase | p < 0.05 | ||||||||||
| Jia et al. [46] |
2016 | Health effects of forest bathing trip on elderly patients with chronic obstructive pulmonary disease | CD8+ T cell number and % | NS | NS | NS | Forest bathing reduces pro-inflammatory cytokine levels, but not proportions of CD8+ T, NK or NKT cells or GrB expression in COPD patients. | Result on perforin expression is questionable, since there is also an effect in control group. | ||||
| NK cell number and % (CD3-CD56+) | NS | NS | NS | |||||||||
| NKT cell number and % (CD3+CD56+) | NS | NS | NS | |||||||||
| Perforin expression in CD8+ T cells (flow cytometry) |
Decrease | p < 0.001 | Decrease | NA | Decrease | p < 0.01 | ||||||
| Perforin expression in NK cells (flow cytometry) |
Decrease | p < 0.001 | Decrease | NA | NS | |||||||
| Perforin expression in NKT cells (flow cytometry) |
Decrease | p < 0.001 | Decrease | NA | Decrease | p < 0.05 | ||||||
| Granzyme B expression in CD8+ T cells (flow cytometry) |
NS | NS | NS | |||||||||
| Granzyme B expression in NK cells (flow cytometry) |
NS | NS | NS | |||||||||
| Granzyme B expression in NKT cells (flow cytometry) |
NS | NS | NS | |||||||||
| IL-6 level in serum | Decrease | p < 0.01 | NS | Decrease | p < 0.05 | |||||||
| IL-8 level in serum | Decrease | p < 0.05 | NS | Decrease | p < 0.01 | |||||||
| IFN-y level in serum | Decrease | p < 0.01 | NS | Decrease | p < 0.05 | |||||||
| IL-1b level in serum | NS | NS | Decrease | p < 0.05 | ||||||||
| CRP level in serum | NS | NS | Decrease | p < 0.05 | ||||||||
| TNFα level in serum | NS | NS | NS | |||||||||
| Kim et al. [52] | 2015 | Forest adjuvant anti-cancer therapy to enhance natural cytotoxicity in urban women with breast cancer: A preliminary prospective interventional study | NK cell number (CD3-CD56+) | Increase | p < 0.01 | Forest therapy enhances natural cytotoxicity in breast cancer patients by increasing NK cells and cytotoxic mediators. | ||||||
| Perforin level in serum (ELISA) | Increase | p < 0.02 | ||||||||||
| Granzyme B level in serum (ELISA) | Increase | p < 0.02 | ||||||||||
| Li et al. [53] | 2007 | Forest bathing enhances human natural killer activity and expression of anti-cancer proteins | NK cell number and % (CD16+) | Increase | p < 0.01 | Forest bathing enhances NK cell activity and numbers in healthy male adults. | ||||||
| Cytolytic NK cell activity (Cr-release assay) | Increase | p < 0.01 | ||||||||||
| % of T cells (CD3+) | Decrease | NA | ||||||||||
| % of perforin- expressing cells |
Increase | p < 0.01 | ||||||||||
| % of granzyme A/B- expressing cells |
Increase | p < 0.01 | ||||||||||
| % of granulysin-expressing cells | Increase | p < 0.01 | ||||||||||
| Li et al. [55] | 2008a | A forest bathing trip increases human natural killer activity and expression of anti-cancer proteins in female subjects | NK cell number and % (CD16+) | Increase | p < 0.01 | Forest bathing enhances NK cell activity and numbers in healthy female adults. | ||||||
| Cytolytic NK cell activity (Cr-release assay) | Increase | p < 0.01 | ||||||||||
| % of T cells (CD3+) | Decrease | p < 0.05 | ||||||||||
| % of perforin- expressing cells |
Increase | p < 0.01 | ||||||||||
| % of granzyme A/B- expressing cells |
Increase | p < 0.01 | ||||||||||
| % of granulysin- expressing cells |
Increase | p < 0.01 | ||||||||||
| Li et al. [54] | 2008b | Visiting a forest, but not a city, increases human natural killer activity and expression of anti-cancer proteins | NK cell number and % (CD16+) | Increase | p < 0.01 | NS | Increase | p < 0.05 | Forest bathing enhances NK cell activity and numbers in healthy adults. | |||
| Cytolytic NK cell activity (Cr-release assay) | Increase | p < 0.01 | NS | Increase | p < 0.05 | |||||||
| % of T cells (CD3+) | NS | NS | ||||||||||
| % of perforin- expressing cells |
Increase | p < 0.01 | NS | |||||||||
| % of granzyme A/B- expressing cells |
Increase | p < 0.01 | NS | |||||||||
| % of granulysin- expressing cells |
Increase | p < 0.01 | NS | |||||||||
| Lyu et al. [47] | 2019 | Benefits of a three-day bamboo forest therapy session on the psychophysiology and immune system responses of male college students | Cytolytic NK cell activity |
Increase | p < 0.05 | NS | NA | Forest bathing in a bamboo forest enhances NK cell activity and percentages in healthy adults. | ||||
| % of NK cells (CD16+CD56+) | Increase | p < 0.05 | NS | NA | ||||||||
| Perforin level (ELISA) | Increase | p < 0.05 | NS | NA | ||||||||
| Granulysin level (ELISA) | NS | NS | NA | |||||||||
| Granzyme A/B level (ELISA) | Increase | p < 0.05 | NS | NA | ||||||||
| Mao et al. [50] | 2012a | Effects of short-term forest bathing on human health in a broad-leaved evergreen forest in Zhejiang Province, China | IL-6 level in serum (radioimmunoassay) |
NS | Increase | NA | Decrease | p < 0.05 | Forest bathing decreases pro-inflammatory cytokine levels (IL-6 and TNFα) in healthy young adults but has no effect on immune cell distribution. | Questionable effect (increase) in control group compared to baseline for IL-6 and TNFα levels. | ||
| TNFα level in serum (radioimmunoassay) | Decrease | NA | Increase | NA | Decrease | p < 0.05 | ||||||
| HCRP level in serum | NS | |||||||||||
| % of B cells (CD5+CD19+) | Increase | p < 0.05 | No pre-intervention data shown for leukocyte distributions. | |||||||||
| % of T cells (CD3+) | NS | |||||||||||
| % of Th cells (CD3+CD4+) | NS | |||||||||||
| % of cytotoxic T cells (CD3+CD8+) | NS | |||||||||||
| % of NK cells (CD3-CD16+CD56+) |
NS | |||||||||||
| Mao et al. [51] | 2012b | Therapeutic effect of forest bathing on human hypertension in the elderly | IL-6 level in serum (radioimmunoassay) |
Decrease | p < 0.05 | NS | NS | Forest bathing decreases pro-inflammatory cytokine level (IL-6, but not TNFα) in elderly patients with hypertension. | ||||
| TNFα level in serum (radioimmunoassay) | NS | NS | NS | |||||||||
| Mao et al. [49] | 2017 | The salutary influence of forest bathing on elderly patients with chronic heart failure | IL-6 level in serum (ELISA) | NS | NS | Decrease | p < 0.05 | Forest bathing decreases pro-inflammatory cytokine level (IL-6, but not TNFα) in elderly patients with chronic heart failure. | No effect in intervention group compared to baseline. | |||
| TNFα level in serum (ELISA) | NS | NS | NS | |||||||||
| HCRP level in serum | NS | NS | NS | |||||||||
| Mao et al. [48] | 2018 | Additive benefits of twice forest bathing trips in elderly patients with chronic heart failure | IL-6 level in serum (ELISA) | NS | NS | NS | A second forest bathing trip further decreases pro-inflammatory cytokine level (TNFα, but not IL-6) in elderly patients with chronic heart failure. | |||||
| TNFα level in serum (ELISA) | Decrease | p < 0.05 | NS | Decrease | p < 0.05 | |||||||
| Seo et al. [56] | 2015 | Clinical and immunological effects of a forest trip in children with asthma and atopic dermatitis | Asthma: | Forest environment improves clinical symptoms in asthmatic children. | ||||||||
| Forced vital capacity (spirometry, FCV) |
Increase | p < 0.05 | ||||||||||
| Fractional exhaled nitric oxide (FeNO) | Decrease | NA | ||||||||||
| Seo et al. [56] | 2015 | Clinical and immunological effects of a forest trip in children with asthma and atopic dermatitis | Atopic dermatitis: | Forest environment improves clinical symptoms and has immunological effects in chronic allergic skin disease. | ||||||||
| Atopic dermatitis index (SCORAD) | Decrease | NA | ||||||||||
| Thymus and activation-regulated chemokine/CCL17 level | NS | |||||||||||
| Macrophage-derived chemokine/CCL22 level | Decrease | p < 0.01 | ||||||||||
| Tsao et al. (forest workers) [57] | 2018 | Health effects of a forest environment on natural killer cells in humans: an observational pilot study | % of NK cells in blood (CD3-CD56+) |
Increase | p < 0.05 | Living in a forest environment increases NK cell percentage, but not the amount of activated NK cells. | ||||||
| % of activated NK cells in blood (CD3-CD56+CD69+) | NS | |||||||||||
| Tsao et al. (forest bathing) [57] | 2018 | Health effects of a forest environment on natural killer cells in humans: an observational pilot study | % of NK cells in blood on d5 | NS | Short-term forest trip enhances fraction of activated NK cells in healthy adults, and effect lasts for at least 4 days. | |||||||
| % of activated NK cells in blood on d5 | Increase | p < 0.01 | ||||||||||
| % of NK cells in blood on d9 (4 days after intervention) | NS | |||||||||||
| % of activated NK cells in blood on d9 (4 days after intervention) | Increase | p < 0.01 | ||||||||||
| BVOC inhalation | ||||||||||||
| Li et al. [58] | 2009 | Effect of phytoncide from trees on human natural killer cell function | Cytolytic NK cell activity (Cr-release assay) | Increase | p < 0.05 | Phytoncide exposure enhances NK cell activity and % in healthy adults. | ||||||
| % of NK cells (CD16+) | Increase | p < 0.01 | ||||||||||
| % of T cells (CD3+) | Decrease | p < 0.01 | ||||||||||
| % of perforin- expressing cells |
Increase | p < 0.05 | ||||||||||
| % of granzyme A/B- expressing cells |
Increase |
p < 0.01 p < 0.05 |
||||||||||
| % of granulysin- expressing cells |
Increase | p < 0.05 | ||||||||||
| Fragrance inhalation | ||||||||||||
| Kiecolt-Glaser et al. [59] | 2008 | Olfactory influences on mood and autonomic, endocrine and immune function | Delayed hypersensitivity to candida (DTH) | Increase | NA | Increase | NA | Decrease | p = 0.02 (lavender) p = 0.06 (lemon) | Greater DTH response after water inhalation indicates better immune response than in fragrance groups, but no difference in cytokine levels detectable. | * Differing effects in blinded and informed groups for blastogenesis responses. | |
| PBL proliferation (blastogenesis) |
NA* | |||||||||||
| IL-6 level in PBLs (ELISA) | NS | |||||||||||
| IL-10 level in PBLs (ELISA) | NS | |||||||||||
| Komori et al. [60] | 1995 | Effects of citrus fragrance on immune function and depressive states | Deviation from normal CD4/CD8 ratio | Decrease | NA | Citrus fragrance has a beneficial effect on immune cell distribution in depressive patients and can reduce the dose antidepressants needed. | ||||||
| Deviation from normal NK cell activity (Cr-release assay) |
Decrease | NA | ||||||||||
| Trellakis et al. [61] | 2012 | Subconscious olfactory influences of stimulant and relaxant odors on immune function | IL-8 level in serum (ELISA) | NS | No significant effect of any stimulatory or relaxing fragrance exposure on immune parameters in healthy adults. | |||||||
| IL-6 level in serum (ELISA) | NS | |||||||||||
| TNFα level in serum (ELISA) | NS | |||||||||||
| CCL3 (MIP-1a) level in serum (ELISA) | NS | |||||||||||
| CCL4 (MIP-1b) level in serum (ELISA) | NS | |||||||||||
| CCL5 (RANTES) level in serum (ELISA) | NS | |||||||||||
| CXCL8 (IL-8) release by neutrophils | NS | |||||||||||
| Waterfall exposure | ||||||||||||
| Gaisberger et al. [35] | 2012 | Effects of ionized waterfall aerosol on pediatric allergic asthma | IL-5 level in serum (ELISpot) | Decrease | p < 0.05 | NS | Decrease | NS | Exposure to waterfalls reduces pro-inflammatory cytokines and allergic asthma symptoms, enhances lung function and induces Treg cells. | |||
| IL-10 level in serum (ELISpot) | Increase | p < 0.05 | NS | Increase | NS | |||||||
| IL-13 level in serum (ELISpot) | Decrease | p < 0.01 | Decrease | p < 0.01 | NS | |||||||
| IL-10 expression (PCR) | Increase | NA | Increase | NA | NS | |||||||
| IL-13 expression (PCR) | Decrease | NA | NS | NA | Decrease | p < 0.05 | ||||||
| IFNg expression (PCR) | Increase | NA | Increase | NA | NS | |||||||
| Treg cells (%) | Increase | p < 0.01 | Increase | p < 0.05 | NS | |||||||
| Eosinophilic cationic protein (ECP) levels in serum | Decrease | p < 0.05 | NS | NS | ||||||||
| Fractional exhaled nitric oxide (FeNO) at d20 | Decrease | p < 0.001 | Decrease | p < 0.001 | NA | |||||||
| Fractional exhaled nitric oxide (FeNO) at d80 | Decrease | p < 0.01 | NS | NA | ||||||||
| Peak expiratory flow rate (PEF) | Increase | p < 0.01 | Increase | p < 0.01 | NA | |||||||
| Other spirometric parameters (FEV, FEV%FVC, FEF25, FEF50, MMEF2575) | Increase |
p < 0.05 p < 0.01 |
NS | NA | ||||||||
| Grafetstätter et al. [34] | 2017 | Does waterfall aerosol influence mucosal immunity and chronic stress? A randomized controlled clinical trial | IgA level in saliva (d6) | Increase | NA | Increase | NA | Increase | p = 0.001 | Exposure to waterfalls activates the immune system and improves lung function. | ||
| IgA level in saliva (d66) | Increase | NA | NS | Increase | p < 0.05 | |||||||
| Peak expiratory flow rate (PEF) (d6) | Increase | p = 0.023 | Increase | NA | NS | |||||||