Forest bathing

Forest bathing as a de-stressing nature activity was created in Japan in the early 1980s as a reaction to the fact that many Japanese became ill from stress, but also because the Japanese forestry commission was looking for new job openings and opportunities for a forestry industry in crisis. However, it would be a long time before forest bathing, and eventually also forest therapy, became established in practice. Only after research studies carried out in the 1990s yielded positive results and a plan was drawn up for national implementation, was it possible to obtain government funding and launch extensive certification of suitable forest areas and training of forest therapists and forest bathing guides. Now the activity is pursued throughout the country, with more than sixty approved forest therapy bases.

The research that has been carried out into forest bathing (amongst other things to establish that a specific forest is, in actual fact, calming) has often been based on taking different physiological and psychological measurements from a number of participants before and after forest bathing. The results have then been compared with measurement data obtained from similarly tranquil stays in an urban environment. There are also studies comparing forest bathing with other health-promoting or calming activities. Measurements have been taken from different groups of people: students, old people, middle-aged people, the stressed, depressed, those with heart disease, COPD patients and others. Most of the research has been carried out in Asia, but now there are more and more studies on the subject coming from other parts of the world as well.

Psychological measurements

Experimental studies and review studies show a positive correlation between nature and well-being (Antonelli et al 2021), mindfulness and mental well-being (Timko Olson et al 2020), mood elevation (Yau and Loke 2020; Furuyashiki et al 2019; Jia et al 2016; Lee et al 2011), as well as spirituality (Hansen 2020). Further research suggests that anxiety levels fall (Yau and Loke 2020; Zhou et al 2019) and that depression, anger, tension, fatigue and confusion are reduced after forest bathing (Muro et al 2022); Wen et al 2019; Li et al 2016).

Comparisons between forest bathing and other methods/activities

When forest bathing was compared to empathy exercises, a relatively established well-being intervention, well-being and heart variability was equally enhanced by both these wellness activities (McEwans et al 2021). Other studies showed that shinrin-yoku performed on-site in the forest, has a greater positive effect than watching filmed forest bathing (Markwell & Gladwin 2020) and that the feeling of vitality and recovery is greater after a ‘forest bath’ in the forest than in an urban environment (Takayama et al 2014).

Physiological measurements

A review of studies shows that forest bathing can improve cardiovascular, haemodynamic (pulse rate, blood pressure, HRV and similar), neuroendocrine and metabolic functions (interaction of the nervous system with hormone-producing organs as well as metabolic rate). It can also have a positive effect on immunity, inflammatory and electrophysiological processes and on antioxidant levels (Wen et al 2019).

The cardiovascular system

According to research, forest bathing has a positive effect on the cardiovascular system (Dogaru 2020). Several studies show that blood pressure drops (Peterfalvi et al 2021; Yau and Loke 2020; Furuyashiki et al 2019) and that heart variability (HRV) and pulse rate indicate that the stress level in the body decreases (Yau and Loke 2020; Lee et al 2011).

Hormones

Forest bathing can reduce the stress hormone, cortisol, which is often measured via saliva (Lee et al 2011; Antonelli et al 2019). Some researchers believe that the reduction in stress hormones may include a placebo effect (Antonelli et al 2019).

Other functions in the body/brain

When the dopamine level in the blood is measured (dopamine is a so-called signal substance that is involved in the reward system in the body), it has been seen to decrease, indicating reduced stress after forest bathing (Li et al 2016). Forest bathers with chronic heart failure have seen that biomarkers for heart failure decrease in the brain, as does inflammatory response and oxidative stress (Mao et al 2018). Immune function-enhancing effects, such as increased activity of so-called Natural Killer (NK) cells (a kind of white blood cell) have also been observed (Peterfalvi et al 2021; Jia et al 2016; Li et al 2007).

Forest bathing over an extended period of time

Most of the research studies are based on study participants engaging in forest bathing for one hour or a few hours. It is therefore a fairly short-term initiative or activity. But there are exceptions. When participants were allowed to engage in forest bathing for four days, samples showed increased levels of natriuretic peptides (which can help lower blood pressure) and antioxidants in the blood, while inflammatory cytokines decreased compared to a corresponding time spent in an urban environment (Mao et al 2017). Students who participated in a three-day forest bathing retreat in another study increased self-compassion, the sense of common humanity and the feeling of conscious presence (mindfulness), but contrary to what many other studies have shown, well-being did not change (Kotera and Fido 2021).

Research into forest bathing – a critical approach

Many of the studies carried out so far on forest bathing are relatively small. It is therefore difficult for researchers to demonstrate statistically significant results. Larger and randomised studies are needed, primarily to reinforce and corroborate the physiological effects. In one review article, the researchers noted frankly that the physiological evidence for the beneficial effects of forest bathing remains inconclusive (Antonelli et al 2021).

The review suggests that the positive results of the research in the area of forest bathing should be taken with a pinch of salt. Many studies that did not yield positive results have never been published. Sometimes researchers have gone to unreasonable lengths to find and demonstrate different connections. One example of the latter (there are many) is a study in which Chinese students were encouraged to forest bathe in similar deciduous forest-like parks containing different species of tree (Guan et al 2017). The results of the study showed that the park containing maples was best at reducing students' anxiety about their studies, whereas their anxiety about future employment decreased most amongst birch trees. Anxiety about the actual lesson situation was lower in the oak forest compared to the birch forest. Women students experienced the least anxiety amongst oaks. Forest bathing was also more anxiety-relieving for students with a higher weight than those with a lower weight.

Are these results even relevant? Perhaps it would have been better just to note that all three forest environments reduced anxiety prior to the studies and that the birch forest was the best – and discount the other somewhat contrived results.

/Text: Ann Dolling