In 1982, Japan turned walking slowly through the woods into a public-health idea called forest bathing. Then it spent decades studying what forests really do to stress, the heart, and the body

Forest bathing arrives in most Western coverage wrapped in the language of ancient wisdom, as though people in Japan had been walking slowly through cedar groves for a thousand years under that name. They had not. As a named practice, it is younger than the personal computer.

The term shinrin-yoku was coined in 1982 by Tomohide Akiyama, then head of Japan’s Ministry of Agriculture, Forestry and Fisheries. It translates loosely as taking in the atmosphere of the forest, and at the start it sat closer to public policy than to spirituality. Japan is roughly two-thirds forest. The country had also spent the 1970s and early 1980s urbanising at speed, under a working culture punishing enough to produce its own word for death by overwork. Akiyama’s idea joined two problems that looked unrelated: a stock of underused national forest, and a population visibly carrying the strain of city life.

What makes shinrin-yoku unusual is that Japan did not stop at the slogan. Over the following decades, researchers set out to measure whether time in a forest does anything the body can actually register. That work is the interesting part, and the part most likely to be misread.

rWhat the field studies actually measured

The most cited physiological work comes from a team led by Bum-Jin Park and Yoshifumi Miyazaki, who ran field experiments in 24 forests across Japan. At each site, small groups spent time walking in and looking at a forest on one day and an urban area on another, with the order reversed as a check. The researchers measured salivary cortisol, blood pressure, pulse rate, and heart rate variability, the last of these a common proxy for the balance between the body’s stress and rest systems.

In the forest, on average, cortisol readings and pulse rates came out lower, and the heart rate variability measures shifted in the direction associated with a calmer state. The result is real, and it is narrow. Most of the subjects were young men, around 280 in total across all the sites, and the measurements captured a short walk, not a life.

This is worth holding onto before the immune findings arrive, because that is where the story tends to get ahead of itself.

The immune finding, and why it gets oversold

Most of the immune claim rests on the work of Qing Li, an immunologist at Nippon Medical School in Tokyo. In a 2007 study, Li took twelve healthy men aged 37 to 55 from Tokyo companies on a three-day trip into forest, and measured the activity of their natural killer cells, a type of white blood cell involved in the body’s response to infection and to tumours.

Their activity rose.

In a follow-up comparing a forest trip with a city trip, only the forest produced the effect, and the researchers reported it persisting more than seven days. Phytoncides, the airborne compounds trees release, were present in the forest air and largely absent in the city.

This is where the widely repeated figure of a roughly 50 per cent rise in natural killer activity comes from. The number is striking, and it travels well, which is part of the trouble. It comes from a handful of studies with very small samples, no blinding, and, in the early work, no control group. A change in a marker measured in twelve people is a reason to keep looking, not the final word.

The tempting leap is from immune marker to protection from disease. The research does not make that leap, and neither should the reader.

What the field says about its own evidence

The most useful assessments of forest bathing come from the people reviewing the field rather than promoting it. A 2019 systematic review in Environmental Health and Preventive Medicine gathered 28 studies and found the methodological quality uneven, with randomised trials scoring meaningfully higher than the rest. A 2024 review of forest bathing and self-directed thinking rated the overall study quality as low, citing small samples and a shortage of randomised, controlled designs. A systematic review and meta-analysis published in Frontiers in Psychology in January 2026 went further, applying the GRADE framework and rating the certainty of evidence across every outcome as very low, mainly because of risk of bias, inconsistency, and imprecision.

None of this means the effect is imaginary. It means the research base is thinner and messier than the confident headlines suggest. Samples skew young, or male, or both. Blinding is nearly impossible when the intervention is a forest, and people who agree to spend a day among trees may already differ from people who decline.

What survives the scepticism

Older research helps steady the picture. In 1984, the environmental psychologist Roger Ulrich published a paper in Science reporting that surgical patients in rooms with a view of trees recovered somewhat faster, and asked for less pain medication, than those facing a brick wall. It was a single study, and a decades-old one, but it pointed at the same modest idea from a different angle: ordinary contact with green space seems to do something measurable, even where the size and the mechanism stay unsettled.

What holds up across the shinrin-yoku work is not the anti-cancer promise but something quieter: short periods in a natural setting tend to leave people calmer, by their own report and on some short-term physiological measures. That is the smaller, more useful claim, since it does not ask anyone to believe a reading from a small blood sample will change how long they live.

Framed that way, the 1982 policy looks shrewd rather than mystical. Akiyama did not need forests to cure anything. He needed a reason for a strained urban population to use them, and a walk that settles your pulse for an afternoon is reason enough.

The boundary worth keeping is simple. For anyone managing a real illness, a forest is a pleasant addition to their care, not a substitute for it, and nothing in this literature suggests otherwise.

The most defensible version of forest bathing is also the least dramatic. Time among trees appears to settle the body a little, for a while. Japan built a national programme on that observation, and forty years of study has mostly confirmed the modest version while leaving the grand one open. A smaller finding than the brochures allow, and a sturdier one for it.