From the Research
Level of Evidence for Forest Bathing on the Immune System
The level of evidence for the effect of forest bathing on the immune system is supported by several studies, including:
- A 2007 study published in the International Journal of Immunopathology and Pharmacology, which found that forest bathing enhanced human natural killer activity and expression of anti-cancer proteins 1.
- A 2008 study published in the Journal of Biological Regulators and Homeostatic Agents, which found that a forest bathing trip increased human natural killer activity and expression of anti-cancer proteins in female subjects 2.
- A 2010 study published in Environmental Health and Preventive Medicine, which found that forest bathing trips resulted in an increase in NK activity, mediated by increases in the number of NK cells and the levels of intracellular granulysin, perforin, and granzymes A/B 3.
- A 2022 study published in Environmental Health and Preventive Medicine, which reported that forest bathing/Shinrin-yoku has beneficial effects on human health, including increasing human natural killer activity, reducing blood pressure and heart rate, and reducing stress hormones 4.
- Another 2022 study published in Environmental Chemistry Letters, which reviewed the effects of forest-bathing and physical activity on limiting the severity of COVID-19 disease and preventing virus infection, and found that forest-bathing may have immunostimulatory effects on the human body 5.
Key Findings
Some key findings from these studies include:
- Forest bathing trips can increase NK activity, which can last for more than 7 days after the trip 1, 2.
- Forest bathing trips can increase the number of NK cells and the levels of intracellular anti-cancer proteins 1, 2, 3.
- Forest bathing/Shinrin-yoku can reduce blood pressure and heart rate, and reduce stress hormones 4.
- Forest-bathing may have immunostimulatory effects on the human body, which can help prevent virus infection and limit the severity of COVID-19 disease 5.
Study Characteristics
The studies that investigated the effect of forest bathing on the immune system had the following characteristics:
- The studies were conducted in Japan and involved healthy male and female subjects 1, 4, 2, 3.
- The forest bathing trips typically lasted for 3 days and 2 nights, and involved walking in forest fields for several hours each day 1, 2, 3.
- The studies measured NK activity, the number of NK cells, and the levels of intracellular anti-cancer proteins, as well as other health outcomes such as blood pressure, heart rate, and stress hormones 1, 4, 2, 3.