Forest Bathing: What Happens in the Body When We Slow Down Among Trees

A walk through the forest often feels like a deep breath for body and mind. In Japan, this feeling was given a name in the 1980s – Shinrin-yoku, or "forest bathing" – and people began to study it systematically. The idea itself, however, is far older in Europe than the term: from air-cure resorts and forest cures to summer retreats in mountain woodland, the calm beneath the trees has been part of the culture of recovery here for generations. What can actually be observed today when people spend time in the forest – and what role do those invisible scent compounds play that conifers and broadleaf trees release into the air?

Where the term "forest bathing" comes from – and why the forest has a long European tradition

The expression Shinrin-yoku was coined in 1982 by the Japanese forestry agency, originally as an invitation to make greater use of the country's woodlands. From this cultural impulse a dedicated field of research later developed, which a group led by the physician Qing Li describes as "forest medicine". What is meant by it is nothing exotic, but rather a conscious, slow stay in the forest – without a goal, without a distance, without pace.

While the term comes from Japan, the practice itself is firmly rooted in Europe. As early as the 19th century, doctors sent those in need of recovery to wooded air-cure resorts; the summer retreat in mountain woodland, the Kneipp tradition and the sanatoria in the high reaches of the Alps all built on the idea that clean forest air and quiet do people good. In Switzerland, around a third of whose land area is forested, this body of experience lies quite literally on the doorstep. Forest bathing is therefore less a new trend than a new name for an old, time-tested European habit.

What terpenes are and how trees release them into the air

The characteristic scent of a coniferous forest is no accident. Trees and other plants release volatile organic compounds known as terpenes. In the context of the forest, researchers often speak of phytoncides – plant messenger substances with which trees defend themselves against micro-organisms and herbivores. Some of these substances reach the air, and it is precisely these that we breathe in as we walk.

Among the most common terpenes in forest air are alpha-pinene, beta-pinene and limonene. They are especially abundant in European conifers such as pine (also called Scots pine), spruce, fir and larch. On warm days and after rain, trees release more of them – one reason the forest smells particularly intense at such times. The overview below places some of the best-known compounds in context.

What research has observed about immune cells and terpenes

The best-known findings on forest bathing come from a series of Japanese studies conducted from 2005 onwards. In a narrative review, Qing Li summarises several small, mostly uncontrolled human studies: after multi-day forest stays of around three days, the activity of so-called natural killer (NK) cells – a group of cells of the innate immune system – was on average higher than before, and in individual studies this difference persisted for about 30 days. An important caveat: these were studies with very few participants, frequently men only, and without a randomised control design.

To examine whether the terpenes in forest air might be involved in these observations, the same group carried out a small experimental human study, listed as a clinical trial. Twelve men stayed in hotel rooms in which tree oil containing phytoncides – including alpha- and beta-pinene – was vaporised through a humidifier. After exposure, NK activity was higher and the urinary concentration of the stress hormones adrenaline and noradrenaline was lower. The authors phrased their result deliberately cautiously: the phytoncides could contribute to the observed change – a study this small does not provide proof of a targeted effect in humans.

What studies show on stress hormones, blood pressure and the nervous system

Beyond immune cells, research focuses above all on stress and relaxation. A systematic review with meta-analysis examined salivary and blood cortisol as a stress marker and found that levels tended to be lower in forest groups than in comparable urban groups. A later review of reviews, produced at LMU Munich, considerably qualifies this finding, however: across all studies the overall effect on cortisol was small and the results highly inconsistent; a statistically clear effect appeared only in subgroups. Both readings belong together – the signal points in one direction, but is less unambiguous than individual headlines suggest.

Blood pressure has also been studied. A systematic review with meta-analysis found that systolic blood pressure after stays in a forest environment was on average around 3 mmHg lower than outside the forest. The authors themselves point out, though, that most of the individual studies had small samples and measured short-term changes. Reviews additionally describe indications of a shift in the autonomic nervous system – towards more activity of the calming parasympathetic and less of the activating sympathetic branch. The table below sets out the areas of evidence together with their limits.

How robust is the evidence really?

As coherent as the overall picture seems, some restraint is warranted in interpreting it. A large share of the studies comes from Japan and neighbouring countries, works with small participant numbers, often men only, and mostly measures short-term changes. The methods differ considerably from study to study, which makes comparisons difficult. Expectation and placebo effects can hardly be ruled out entirely, especially with an "intervention" as pleasant as a forest walk. The Munich review of reviews therefore reaches a sober conclusion: the indications of relaxing and stress-reducing effects are real, but solid proof of clearly defined, lasting health effects is still outstanding.

Placed sensibly in context, this means: forest bathing is an accessible, low-cost and low-risk way to spend time in nature, for which short-term calming signals are well documented. It does not replace medical treatment – it can complement a healthy everyday life, but cannot substitute for medical therapy or prescribed medication.

Safety, practice and who forest bathing is suitable for

Forest bathing requires neither equipment nor prior knowledge. In practice it is enough to take your time, walk slowly, put the phone away and direct the senses consciously towards sounds, smells and light. Even twenty minutes can be enough; there is no distance to cover and no goal to reach. For the vast majority of people this is entirely safe.

A few practical points are nonetheless worth noting. Anyone sensitive to pollen should choose times of day and seasons with lower exposure. In Swiss forests, ticks are something to bear in mind – long clothing and checking the skin after the walk make sense. For children, the forest is well suited as a natural space for movement and discovery, ideally with company. During pregnancy and breastfeeding there is usually nothing to be said against quiet walking; where there is uncertainty, a question to a doctor brings clarity. People with cardiovascular conditions or elevated blood pressure can use forest walks as part of a healthy lifestyle, but should continue their medically prescribed treatment unchanged.

When the forest isn't reachable every day: the European herbal tradition

Not everyone can get into the forest every day. The city, the working routine and the season set limits, while the need for moments of inner calm remains untouched by them. Here it is worth looking at European plant lore, which knew its own ways of finding calm long before the term forest bathing existed. Tradition-rich plants such as lemon balm, lavender and passionflower have accompanied the central European and Mediterranean herbal tradition for centuries.

Micronutrients additionally play a part in the body's ordinary physiology: magnesium contributes to the normal functioning of the nervous system, and vitamin B6 to normal psychological function. For anyone who cannot always fit in a daily forest walk, a well-conceived European herbal combination with selected micronutrients offers an approach that can fit into one's own routine.

What can be said – and what remains open

Research on forest bathing paints a cautiously positive picture. The signals are most consistent for short-term relaxation and stress reduction: lower stress hormone levels, slightly lower blood pressure and a shift in the autonomic nervous system towards calm. The observations on immune cells are fascinating, but rest on very small studies, and the role of the terpenes is plausible yet not conclusively proven. The most honest way to describe forest bathing is as what it is: a pleasant, accessible and low-risk way to spend time in nature, with measurable short-term signals of calm. That Japanese research and the old European tradition of woodland recovery arrive at the same point here makes the matter no less interesting.

This article is for general information and does not replace medical advice. Food supplements are not a substitute for a balanced, varied diet and a healthy lifestyle. In the case of health complaints, during pregnancy and breastfeeding, and when taking medication, please consult a doctor.