The science of forest bathing: Nature’s prescription

In recent years, the practice of shinrin-yoku — also known as forest bathing — has garnered worldwide attention for its psychological and physiological benefits. 

It is well known that spending time in nature and practicing mindfulness can each profoundly improve overall health. A growing body of research supports the idea that their convergence into a single activity, known as forest bathing, has an even greater health benefit. Originating in Japan in the 1980s, forest bathing is a form of ecotherapy that involves completely immersing oneself in a forested environment. The practice is more than just a peaceful walk in nature — it is an intentional, mindful experience that requires being fully aware of one’s environment and doing activities to engage all their senses with nature.

Recent research reveals that forest bathing can improve mood while decreasing feelings of depression and anxiety.  Studies have shown that forest bathing for just two hours a week can result in a statistically significant decrease in depressive tendencies. Its mental health benefits are so profound that some physicians in countries like Japan and South Korea have begun prescribing forest therapy to patients with major depressive disorder or various stress-related conditions. Physiologically, forest bathing can lower stress hormone levels, boost immune function, and elevate serotonin in the blood, leading to reduced stress, improved mood, and even lower blood pressure.

A critical element of forest bathing’s health benefits lies in the forest air itself, which is rich in natural compounds called phytoncides. These are volatile organic compounds released by trees and other plants that serve as a defense mechanism against insects and bacteria. They contribute greatly to human health benefits experienced as a result of forest bathing.

“A critical element of forest bathing’s health benefits lies in the forest air itself, which is rich in natural compounds called phytoncides.”

Perhaps the most significant of phytoncides’ benefits is their impact on the immune system. In a 2006 study, a team of researchers at Nippon Medical School found that exposure to forest air rich in phytoncides significantly increases the activity of natural killer (NK) cells, a type of white blood cell that plays a crucial role in the body’s immune defense against infections and tumors. In a similar 2007 study from Nippon Medical School, a two-day forest bathing experience led to a 53.2% and 50% increase in participants’ NK cell activity and quantity, respectively, and an overall increase in expression of intracellular anti-cancer proteins. Participants maintained enhanced NK cell and anti-cancer protein activity for up to 30 days after, which indicates long-lasting immune-boosting effects. Evidence also shows that the benefits of phytoncides persist even beyond natural environments. In a 2023 study, researchers at Chungnam National University found that phytoncide-rich air had the same effect on participants when inhaled in a laboratory setting. Participants had a 9% reduction in stress hormones, reported feeling less stressed overall, and exhibited a significant increase in NK cell quantity. 

How, exactly, do phytoncides affect the immune, nervous, and endocrine systems? Earlier this year, researchers from Trent University found that phytoncides activate the autonomic nervous system by stimulating the olfactory bulb, a mass of tissue above the nasal cavity, upon inhalation.  This activation causes the parasympathetic nervous system, which controls the rest and digest response, to dominate the sympathetic nervous system, which is responsible for the fight or flight response. The team found an average 17% decrease in sympathetic activity and a corresponding 17% increase in parasympathetic activity in participants. As the body relaxes, this system shift leads to reduced levels of stress-related hormones, including adrenaline, noradrenaline, and cortisol. Stress hormones inhibit NK cells, so their decrease allows NK cells to proliferate, enhancing overall immune function.

As research on forest bathing continues to grow, it is becoming evident that time spent in nature offers more than just a temporary escape — it can lead to meaningful, long-lasting improvements in both mental and physical health. By reducing stress hormones, enhancing immune function, and decreasing feelings of depression and anxiety,  forest bathing provides a unique and accessible way to nurture holistic well-being.