Several theories have been proposed as to why spending time in forests might provide health benefits. Some have suggested that chemicals emitted from trees, so-called phytoncides, have a physiological effect on our stress levels. Others suggest that forest sounds — birds chirping, rustling leaves — have a physiologically calming effect. Yet evidence to support these theories is limited.

On a recent visit to Japan, I met with Dr. Hiroko Ochiai, a surgeon based at Tokyo Medical Center, and her husband, Toshiya Ochiai, who is currently the chief executive of the International Society of Nature and Forest Medicine. Dr. Ochiai is trained in forest therapy and currently conducts most of her sessions with volunteers within a forest in Nagano, about three hours from Tokyo, with the help of a local guide, and plans to offer forest therapy soon at one of Tokyo’s largest hospitals.

“I usually encourage participants to sit or lie down on the forest ground and listen to the sounds,” she says. “The hypersonic natural world can be soothing, and things are always moving even while we are still. It can be very calming.”

Last June the Northside Hospital Cancer Institute in Atlanta began to formally offer forest therapy as part of a pilot project in collaboration with the Chattahoochee Nature Center. Twelve patients with newly diagnosed cancers recently signed up for a session, according to Christy Andrews, the executive director of Cancer Support Community Atlanta.

“It was a four-hour session that seemed to have an impact on the patients,” she said. “I remember one participant telling me afterward that it was a way to ‘steer away from cancer,’ and the group became very cohesive. I think it helped reduce the isolation in a way that’s different from a regular support group.”

Dr. Suzanne Bartlett Hackenmiller, an obstetrician-gynecologist based in Cedar Falls, Iowa, began guiding patients in her practice through the Prairie Woods in Hiawatha Iowa, though she has also led groups in forests around Des Moines. She became a certified guide through the Association of Nature and Forest Therapy three years ago and tries to tailor her offerings based on the group she is leading.

“I generally get a sense of where people are at. For some, it’s best for me to stick to the science, but others may literally want to hug a tree. The traditional tea ceremony at the end might turn some people off, so I’m conscious of that and adjust accordingly,” she says.