Although the Grimm Brothers’ tale of Hansel and Gretel surviving alone in the woods after being abandoned by their parents is based on a grim reality – the famine of 1315-1317 – there are compelling reasons to take kids into a forest today. As long as they are kept out of the clutches of evil witches, and are brought to their respective homes right afterward.

Research on the health benefits of being in a forest environment is so compelling that urban daycares in Finland “built” forests for kids to use. As part of a study on childhood immune systems and overall health, these ersatz woodlands were made by spreading topsoil over play yards, which had been either gravel or concrete. The soil was then planted with native trees, shrubs, and flowers. For obvious reasons, gingerbread houses were not included in the forest plots.

The idea that immersion in nature helps us feel good is old news, of course. Patients in rooms with tree views have shorter hospital stays and report less pain as compared to those who do not have access to a natural vista. University students have been found to score higher on cognitive tests when their windows face natural settings.

Evidence goes far beyond casual observations, however. Over the past two decades, real-time brain imaging with functional MRI and PET scans, as well as blood-cortisol levels, and heart rate and blood pressure measurements have been used in a host of studies on the benefits of being close to nature. Science has demonstrated that spending time in the woods is so helpful that many doctors are now recommending “forest bathing,” which is simply 20 minutes a day spent in the woods. Forest immersion is prescribed along with medications to treat anxiety, pain, high blood pressure, depression, and other ailments. Controlled studies have also revealed that after just an hour in the woods, memory performance and attention span improve by 20%.

Older research has shown improvements in the eyesight, brain development, and mental health of children exposed to nature. But it seems that no one looked closely at the effect of nature on children’s immune systems until a couple of years ago. A four-week study conducted in 2020 through the University of Helsinki compared a number of immune markers in 3-, 4-, and 5-year-olds at ten daycares throughout the urban core of Helsinki. Four of the ten daycares had been greened-up with mini-forests, while the rest were conventional city play-lots, either paved or covered in gravel.

After just 28 days, the gut and skin microbial communities of children who played in nature was more diverse than it was at the beginning of the project. A higher diversity of skin microbes is correlated with stronger immune systems. To be specific, and maybe too technical, the “nature kid” group had lower levels of a protein called Interleuken-17A, which is linked to autoimmune diseases. They also had elevated blood T-cell counts as compared to their initial baseline and to the group that didn’t get a chance to play in the woods and eat dirt, or at least get dirt on them.

The University of Helsinki study, which you can find in the journal Science Advances, includes a statement by the authors that “The results of this study support the hypothesis that low biodiversity in the modern living environment may lead to an un-educated immune system and consequently increase the prevalence of immune-mediated diseases.” There we have it: among other perks, the forest educates our immune systems.

While the research is definitely Finnish, it’s not really finished. The scientists agree more work is needed. They recommend a larger study (this one had 75 children participating) to confirm their findings, and also say that while they’ve shown being in nature gives kids healthier immune systems, they do not yet know exactly how or why it happens.

We need to think of communion with nature as an essential part of our health, and act accordingly. I encourage everyone to start forest-bathing as soon as possible for lower blood pressure and smarter immune systems. And we should get Hansel, Gretel and all other children out in the woods more often, too. Just don’t leave them there.

Paul Hetzler is relieved to have another excuse for a dirty house. He thanks Laurent Dubois for suggesting this topic.