Time in nature eases stress, but forest bathing’s immune claims rest on small studies

Key takeaways

• The chief of Japan’s Forestry Agency coined the term shinrin-yoku, or forest bathing, in 1982 to describe taking in the forest with all five senses².
• A 2022 analysis of 21 studies with 2,270 people found that forest programs lowered blood pressure by about 3 points compared with city settings, with bigger drops in older people and those who started higher⁶.
• The famous claim that forests boost the immune system traces largely to a 2007 study of 12 men, and a 2021 review found that 7 of 13 studies on the question had 20 or fewer people²⁴.
• People who feel more connected to nature report somewhat higher well-being, and noting three good things in nature each day for five days strengthened that bond in one study⁸⁹.
• U.S. neighborhoods that federal officials redlined in the 1930s had less greenery in 2010 than neighborhoods graded “best”¹¹¹³.

For nearly a decade, patients recovering from gallbladder surgery at a suburban Pennsylvania hospital went into whichever room came open¹. Some rooms looked out on a small stand of leafy trees. Others faced a brown brick wall¹.

Roger Ulrich later matched 23 pairs of these patients by sex, age, smoking, weight and other factors, then compared their hospital records from 1972 to 1981¹. All had surgery between May and October, when the trees were in leaf¹.

On average, the tree-view group left the hospital after 7.96 days, while the wall-view group stayed 8.70¹. Nurses’ notes about the tree-view patients were less often negative (an average of 1.13 per patient, against 3.96)¹. From day two through day five, these patients also needed fewer doses of moderate and strong pain medicine¹.

The study, published in Science in April 1984, had just 46 patients and was not a randomized trial¹. Ulrich himself warned that a dull wall isn’t the only alternative to trees, and that a lively street might do more for a bored patient than a natural scene¹.

Still, it raised a question researchers are still working on: what does contact with nature do for us? Four decades later, the honest answer is that it does something real, but less than the hype suggests. We walk through what the evidence shows, starting with the practice that made the question famous.

Forest bathing began in Japan as an invitation to slow down

In 1982, Tomohide Akiyama, then chief of Japan’s Forestry Agency, coined the term shinrin-yoku². It translates as forest bathing: taking in the woods through all five senses, for relaxation².

It isn’t hiking or exercise. There’s no summit and no step count. The idea is to move slowly, pause often and let sights, sounds, smells and textures hold your attention.

The timing served two needs. Many Japanese workers were falling ill from stress, and the struggling forestry sector was looking for new kinds of work³. Research in the 1990s gave the idea scientific footing, and a national rollout followed, with certified forest sites and trained guides³.

Government money came too: ¥150 million in research grants in 2004². Today a Japanese nonprofit, the Forest Therapy Society, certifies about 60 forest therapy bases, where a standard guided session runs about two hours².

The idea fits natural-health values closely. It asks nothing of you but attention, costs little, and treats the living world as a partner in health rather than a backdrop. For many readers, it names something they already practice on a porch, in a garden or along a creek.

The immune claim rests on a dozen tired men

The most repeated forest bathing claim is that tree air strengthens your immune system. It traces largely to Qing Li of Nippon Medical School².

His best-known experiment, published in 2007, was tiny. A dozen worn-out but healthy office workers from Tokyo, aged 37 to 55, spent two nights among the beech forests of Nagano Prefecture². Afterward, their blood held more natural killer (NK) cells, a type of immune cell, and those cells were more active².

A year later, the volunteers made a comparable trip to Nagoya, a city with far less greenery. This time their immune cells didn’t budge².

Could the smell of trees alone do it? For a 2009 study, Li vaporized cypress oil in hotel rooms where volunteers stayed, and the scent by itself made some difference². He credits these airborne plant chemicals, called phytoncides, with roughly 30% of forest bathing’s effect. That’s his personal estimate, and he acknowledges that much remains unexplained².

A 2021 systematic review, which gathers and grades all the studies on a question, looked at 13 studies of forest programs and immune function⁴. Seven had 20 or fewer participants⁴. Only three were randomized trials, where people are assigned by chance to one group or another, and all three raised some concerns about bias⁴.

NK cell numbers rose in six of nine studies that measured them, and NK activity changed in seven of eight⁴. T cells, another kind of immune cell, mostly didn’t change⁴. In one of Li’s studies of women, the rise lasted up to seven days; a study in men reported effects up to 30 days⁴.

Those are real signals worth following up. But the studies measured immune cells in the blood. They didn’t test whether people caught fewer colds or developed fewer cancers.

If you see bottled “forest” oils sold for immunity, remember that the scent evidence rests on one small hotel study².

Calmer bodies: the stress evidence is broader, but messy

Blood pressure and stress hormones have more research behind them. A 2022 meta-analysis, which pools results from many studies into one estimate, compared forest programs with city settings⁶.

Across 21 studies and 2,270 people, forest time lowered the top blood pressure number by about 3.4 points and the bottom number by about 3.1⁶. Across 13 studies with 1,786 people, it also lowered cortisol, a stress hormone, measured in saliva⁶.

The averages hide a lot of variation. Results differed so much from study to study that in some settings the benefit could disappear⁶.

Three patterns stood out⁶:

• Older people and those with higher starting blood pressure saw larger drops.
• Sessions of 20 minutes or longer worked better than shorter ones.
• Sitting and looking worked about as well as walking.

Earlier reviews were more cautious. A 2017 review found six randomized trials with 323 adults and rated all six at high risk of bias; none blinded participants⁵. In one, a Swedish trial of people with exhaustion disorder, a waiting-list group improved just as much on stress, anxiety and depression⁵. A 2019 review of cortisol studies by Antonelli and colleagues found drops after forest bathing, though some researchers suspect a placebo effect, according to a summary by Sweden’s Nordic Nature Health Hub³.

The same summary flags three weak spots: the research is concentrated in Asia, studies tend to be small, and trials with disappointing results may never have reached print³. It describes steady positive findings for mood and well-being, while a review it cites called the evidence on body measures inconclusive³.

Why green places may restore a tired mind

Researchers have offered two main explanations.

The first is about stress. In his 1984 paper, Ulrich pointed to lab studies showing that natural scenes tend to stir positive feelings, ease fear in stressed people and hold attention, which may crowd out worried thoughts¹.

The second is about focus. Attention restoration theory holds that deliberate concentration is a limited resource that tires with use, and that restful settings, often natural ones, help it recover¹⁵. A 2018 review of more than 40 studies that used objective thinking tests found that nature exposure improved working memory and mental flexibility⁷. Effects on attention control were less reliable, and all the effects were small to moderate⁷.

An earlier review had found the evidence for this theory ambiguous, so the 2018 results are a partial vindication, not a final verdict⁷. Real nature may work better than videos or pictures, though real exposures in these studies also tended to last longer⁷.

Nature may also quiet rumination, the habit of replaying the same negative thoughts. In a 2015 Stanford study, volunteers randomly assigned to a 90-minute nature walk showed lower activity afterward in a brain region tied to brooding, while a city walk group did not¹². Their self-reported brooding also fell, though the difference between the two groups came up just short of statistical significance¹².

Our hiking article covers that study’s other limits. One more worth knowing: all 38 volunteers were healthy, with no mental health diagnoses, so it can’t tell us what nature walks do for depression¹².

Feeling connected may matter as much as minutes outside

Researchers increasingly measure nature connectedness: how close and connected you feel to the natural world. The University of Derby’s nature connectedness group, in England, points to evidence that this bond matters for well-being beyond simply spending time outdoors¹⁰.

A meta-analysis by Derby researchers pooled studies of this link⁸. Across 20 samples with 4,758 people, more connected people reported more of the “functioning well” side of well-being, such as personal growth⁸. Across 30 samples with 11,638 people, they also reported more of the “feeling good” side⁸.

Both links were small, with correlations of 0.24 and 0.20 on a scale where 1 is a perfect match⁸. Personal growth stood out, with a moderate link⁸. These are correlations, so they can’t show which comes first.

Can you build connection on purpose? In a 2017 study, 50 people wrote down three good things they noticed in nature each day for five days, while 42 others wrote down three factual things⁹. The nature group’s connectedness rose and stayed higher, and those whose connection grew most also reported better psychological health⁹.

The Derby group describes five pathways into that bond: using your senses, feeling emotion, noticing beauty, finding meaning and caring for nature¹⁰. You’ll see all five in the guided walk below.

Green space isn’t shared equally

Not everyone has trees outside the window. In the 1930s, a federal agency called the Home Owners’ Loan Corporation graded city neighborhoods for lending risk, partly by the race of the people living there, and outlined “hazardous” areas in red¹³.

In 2021, researchers from the University of California and Columbia University compared those maps with satellite images from 2010¹¹¹³. Across 4,141 graded neighborhoods in 102 U.S. urban areas, greenery scores fell step by step with the old grades, from 0.47 in “best” A neighborhoods to 0.36 in redlined D neighborhoods¹¹. The gap held after the team accounted for ecological region and 1940 census conditions¹¹.

Redlining was outlawed in 1968¹³. Its effects on city landscapes have lasted far longer. The study was funded by the Environmental Protection Agency and the National Institutes of Health¹³.

If your block is short on green, the planner below includes options that work on a city street or indoors. Our outdoor exercise article covers park access across U.S. cities.

Plan your nature dose, and try a forest-bathing walk

This planner is our own. The 20-minute level reflects the 2022 finding that longer sessions did better⁶. For the two-hour weekly target, see our outdoor exercise article.

Dose	In the city	Rural or suburban	Indoor fallback
5 minutes a day	Notice three good things in nature on a regular walk, such as a street tree, sky or birdsong	Step outside with your morning drink and listen	Sit by a window with a view of trees or sky
20 to 30 minutes, 2 or 3 times a week	Sit or stroll in the nearest park, cemetery or tree-lined street	A woodlot, field edge or riverside path	A seat near houseplants, or nature photos and videos when you can’t get out
About 2 hours a week	Weekend visit to a large park, arboretum or greenway	A longer forest walk or a garden session	Not a substitute; save indoor options for bad-weather days

A guided forest-bathing walk (30 to 45 minutes)

1. Arrive. Pick a short loop with trees. Silence your phone. Agree with yourself that there’s no destination.
2. Land. Stand still for two minutes. Feel your feet on the ground and let your breathing slow on its own.
3. Walk slowly. Move at about half your normal pace. Each few minutes, shift to a different sense: what you see, hear, smell, then feel.
4. Notice beauty. Stop at anything that catches your eye, such as bark, moss or light through leaves, and look at it for a full minute.
5. Sit. Find a spot and stay for 10 minutes. Watch what moves.
6. Find meaning. Ask what this place has been doing all season while you were busy.
7. Give back. Before you leave, pick up a piece of litter or simply thank the place. Write down three good things you noticed.

Stay on marked paths, and leave plants and fungi where they grow.

How strong is the evidence?

Claim	Rating	What it rests on
Forest time lowers blood pressure and salivary cortisol a little	Promising but early	Pooled studies with large variation; earlier trials at high risk of bias56
Forest bathing improves mood	Promising but early	Many small studies; mood findings mostly positive, though some comparison groups did as well35
Forest bathing boosts immune cells in the blood	Promising but early	Mostly small, non-randomized studies24
Forest bathing prevents infections or cancer	Not enough evidence	Studies measured blood markers, not illness4
Nature improves working memory and mental flexibility	Promising but early	Review of experiments; small to moderate effects7
Feeling connected to nature goes with higher well-being	Promising but early	Correlations from pooled studies; small effects8
A hospital window view speeds surgical recovery	Not enough evidence	One small, non-randomized records study from 19841

Safety basics, and when nature isn’t enough

Time in nature is low risk, and no adverse events were reported in the six trials of the 2017 review⁵. Before longer outings, read the tick advice in our hiking article and the heat, smoke and storm rules in our outdoor exercise article.

Nature can lift a mood, but it isn’t a treatment for mental illness on its own. The National Institute of Mental Health (NIMH) advises getting help if you have severe or distressing symptoms for two weeks or more, such as¹⁴:

• trouble sleeping;
• changes in appetite or unplanned weight change;
• trouble getting out of bed because of your mood;
• trouble concentrating;
• losing interest in things you usually enjoy;
• irritability, frustration or restlessness.

If you or someone you know is struggling or having thoughts of suicide, call or text 988, or chat at 988lifeline.org. The 988 Suicide & Crisis Lifeline is free, confidential and available 24/7. If a life is in danger, call 911¹⁴.

Questions readers ask

The bottom line

Time among trees calms many people, and the research mostly agrees, with modest drops in blood pressure, stress hormones and brooding. The bigger promises, like strong immune boosts from forest air, rest on small studies that measured blood markers, not health.

You don’t need a certified forest or a perfect study to begin. Take five minutes to notice, build to 20, slow down when you’re out there, and pay attention to how you feel. If low mood hangs on for weeks, nature can be part of your care, alongside a professional.

Related reading

• How to move more outdoors when most time in parks is spent sitting
• Hiking can double a walk’s workout, and the way down needs a plan too
• Mindful walking eased stress in small trials, and the walking itself deserves some credit
• Community gardens passed a rare scientific test, so test the soil too
• Fresh air may help you sleep, and a carbon monoxide alarm can save your life

Sources

1. Ulrich RS. “View Through a Window May Influence Recovery From Surgery.” Science, 1984;224(4647):420-421 (copy hosted by the University of Arizona Water Resources Research Center). wrrc.arizona.edu
2. Otake T. “The Science of Shinrin-Yoku: Why Forest Bathing Feels Good.” The Japan Times, June 21, 2025 (copy hosted by Nippon Medical School).
3. Dolling A. “Forest Bathing.” Nordic Nature Health Hub, Swedish University of Agricultural Sciences, updated February 2, 2023.
4. Chae Y, Lee S, Jo Y, Kang S, Park S, Kang H. “The Effects of Forest Therapy on Immune Function.” International Journal of Environmental Research and Public Health, 2021;18(16):8440. pubmed.ncbi.nlm.nih.gov
5. Oh B, Lee KJ, Zaslawski C, et al. “Health and Well-Being Benefits of Spending Time in Forests: Systematic Review.” Environmental Health and Preventive Medicine, 2017;22:71 (Harvard DASH). dash.harvard.edu
6. “The Effects of Forest Therapy on the Blood Pressure and Salivary Cortisol Levels of Urban Residents: A Meta-Analysis.” International Journal of Environmental Research and Public Health, 2022;20(1):458 (PubMed abstract). pubmed.ncbi.nlm.nih.gov
7. Stevenson MP, Schilhab T, Bentsen P. “Attention Restoration Theory II: A Systematic Review to Clarify Attention Processes Affected by Exposure to Natural Environments.” Journal of Toxicology and Environmental Health, Part B, 2018;21(4):1-42 (abstract, Capital Region of Denmark research portal). research.regionh.dk
8. Pritchard A, Richardson M, Sheffield D, McEwan K. “The Relationship Between Nature Connectedness and Eudaimonic Well-Being: A Meta-Analysis.” Journal of Happiness Studies, 2020 (University of Derby repository). doi.org
9. Richardson M, Sheffield D. “Three Good Things in Nature: Noticing Nearby Nature Brings Sustained Increases in Connection With Nature.” PsyEcology, 2017 (University of Derby repository). repository.derby.ac.uk
10. University of Derby Nature Connectedness Research Group. “Evidence Summary.”
11. Nardone A, Rudolph KE, Morello-Frosch R, Casey JA. “Redlines and Greenspace: The Relationship Between Historical Redlining and 2010 Greenspace Across the United States.” Environmental Health Perspectives, 2021 (eScholarship, University of California). pubmed.ncbi.nlm.nih.gov
12. Bratman GN, Hamilton JP, Hahn KS, Daily GC, Gross JJ. “Nature Experience Reduces Rumination and Subgenual Prefrontal Cortex Activation.” Proceedings of the National Academy of Sciences, 2015;112(28):8567-8572 (university-hosted copy). pubmed.ncbi.nlm.nih.gov
13. Columbia University Mailman School of Public Health. “Historically Redlined Neighborhoods Are More Likely to Lack Green Space Today: Study.” January 27, 2021. publichealth.columbia.edu
14. National Institute of Mental Health. “Caring for Your Mental Health.” Last reviewed April 2026. nimh.nih.gov
15. North American Association for Environmental Education, eePRO Research Library. “Attention Restoration Theory II: A Systematic Review to Clarify Attention Processes” (summary of Stevenson et al., 2018). eepro.naaee.org