What are the health benefits of forest bathing?
Walking in the forest regularly measurably reduces anxiety, low mood, and stress. There are positive signals for blood pressure and the immune system, though the evidence there is less clear-cut.
Forest bathing, or shinrin-yoku as it is called in Japan, has the most well-supported effect on anxiety and depression. Many studies combined, covering more than 3,500 participants across 36 studies, show a clear reduction in anxiety and depression scores. This is also the most consistent finding.
Stress hormones such as cortisol (a substance your body produces when you are under stress) and adrenaline measurably fall during forest bathing, and your nervous system shifts more towards a relaxed state. Walking in the forest works most consistently of all forest activities in this regard, and also benefits concentration, memory, and inflammation in the body.
For blood pressure and heart rate the picture looks positive, particularly in older adults. The effect is, however, less clear-cut than the psychological effects. Ten studies in people aged 60 and older also show improvements in heart and lung function and quality of life, but the evidence is too limited for firm conclusions.
Forest bathing also increases the activity of certain immune cells. In a small study with 12 men, that activity rose by around 50% after three days in the forest. A claim made on the back of this, that forest bathing prevents cancer or COVID-19, goes far beyond what the data actually show. That claim comes from a researcher with ties to the Japanese Forest Therapy Society and is speculative. Preventing illness through forest visits has not been demonstrated.
Finally, even looking at photos or videos of nature at home already produces measurable relaxation responses in the body. This suggests that visual contact with nature plays a role in itself, although that is a different effect from actually being in a forest.
This answer draws on several combined overviews of the literature and a large pooled analysis of 36 studies. The researchers themselves caution, however, that most of the studies they analysed carried a high risk of skewed results, and that the activities, durations, and frequencies examined varied widely. This makes it difficult to say which particular type of forest bathing delivers the most benefit. The evidence for psychological effects is stronger than for physical effects. The evidence for immune effects and sleep is thin and comes from small studies.