How ‘forest bathing’ keeps lungs healthy

During the COVID-19 pandemic, Italian scientists documented something interesting: in areas with more trees per capita, the number and severity of COVID-19 cases were lower than in places with fewer trees, even when accounting for differences in human population density1. This work is part of a growing body of research around the world investigating whether time spent in forests and nature can provide protection from infections, such as COVID-19 and pneumonia; inflammatory conditions, such as asthma, emphysema and bronchitis; and even cancer.

‘Touch grass’ has become the rejoinder to stop using electronic devices and to go outside. It’s part of a long-held belief that nature is good for us. The ancient Celts prescribed time sitting next to certain plants as medicine for particular ailments, says conservationist Melinda Gilhen-Baker at the Canadian Parks and Wilderness Society in Ottawa. In Japan, forest bathing (shinrin-yoku) is the traditional practice of spending time in the woods for one’s health.

That culture spurred a Tokyo-based research team to establish the field of forest medicine. Now Japan has adopted it as a national health strategy, with therapy bases in forests across the country. South Korea also operates at least 76 ‘healing forests’, and integrates forest therapy — guided slow walking, deep breathing or meditation in forests — into its National Health Insurance Service. Physicians in other countries, including the United States and the United Kingdom, are also prescribing forest time.

Forests and nature are widely known to buffer humans from respiratory conditions, such as asthma, that are exacerbated by air pollution from cars and industry. Forests are mostly free of these pollution sources, and particles that drift in from urban areas are intercepted by leaves. Forests are also cooler than cities, thanks to the water vapour that plants release during photosynthesis. Higher urban temperatures combined with pollution can form smog, which causes respiratory distress.

Expanses of wilder nature — areas largely inaccessible to people — also shield humans from diseases carried by other animals. Human activities, including the felling of one-third of the world’s forests, have degraded more than 75% of land on Earth, threatening its ability to sustain the lives of plants and animals, including humans. As people push into areas where wild animals live, they can come into contact with new diseases, says Gilhen-Baker. Outbreaks of diseases, such as COVID-19, are becoming more common, and some scientists suggest that forest restoration could provide protection.