Grass Valley Aikikai

Forest bathing: the science in the trees

From: Heat and hydration, forest bathing, and another disease carried by ticks
The CA Dose, June 11, 2026
MATT WILLIS

In medical training we had a word for patients who talked about energy fields, crystals, or the healing power of the forest: woo-woo. It wasn’t kind, and it wasn’t helpful. Since then I’ve learned a lot. One by one, practices that once seemed “out there” to me have gained a stronger evidence base, and I’ve taken some on for my own health. Forest bathing is one.

Shinrin-yoku—“forest bathing” in Japanese—was introduced as a public health practice in Japan in 1982. It basically means being in the presence of trees, walking slowly, breathing deeply, absorbing the forest environment without an agenda. It sounds pretty woo-woo, but there’s good data behind it.

What the data show:

Reduced stress. A systematic review of 131 studies found that cortisol levels—the body’s primary stress hormone—were consistently lower after forest exposure compared to control groups. Forest bathing also reduces blood pressure and heart rate. It increases the activity of parasympathetic nerves—the “rest and digest” system—while calming the sympathetic “fight or flight” system.
Improved immune response. A meta-analysis found that forest bathing increases natural killer (NK) cell activity, which boosts immune response and helps fight infections. The mechanism appears to involve phytoncides—aromatic volatile compounds released by trees.
Improved cognition. Multiple studies have found that children with attention deficit disorder focus better after time in natural settings, with green growing things—on top of the known benefits of activity and movement for regaining focus.
California’s underutilized prescription. We don’t have a pharmaceutical that lowers cortisol, calms the autonomic nervous system, boosts immune cell activity, improves mood, and supports attention—at no cost, with no side effects. My residency self would have called forest bathing woo-woo. My epidemiologist self calls it an intervention with a favorable evidence base and few barriers to access.

We’re fortunate in California to have remarkable nature around us, including our forests. Old-growth redwoods, chaparral hillsides, pine forests throughout the mountains, and parks in most communities. Most Californians live within an hour of green space. Find some trees, breathe slowly, and rest assured the data are on your side.

Our Mountain Weapons Seminar with Steve Thoms Shihan is coming up! Please let us know if you will need housing or a camping space. Call/text (530) 274-1453 or email [email protected] to register. See you soon!

“After”

Progress!

First class on the new mat!
Now everything in the dojo needs to be moved onto the mat to make way for carpet and vinyl flooring to be installed next week. Marci Martinez made a temporary kamiza…