How Being In The Forest Actually Boosts Immunity, According To Science
New research, like the Journal of Adolescent Health study that found that teens who have more access to green space tend to be happier, continues to reinforce the idea that humans are intricately connected to the natural environment. Our entire body is constantly communicating and acting in tandem with our surroundings. But how can something as simple as spending time outside possibly make us healthier? Let's dive into the science.
The real reason being outside is so healing.
The Japanese tradition of Shinrin-yoku, "taking in the forest atmosphere" or "forest bathing," is proof of concept. In this case, the term "bathing" does not mean swimming in some sort of wooded lake. Instead, it's about diving into a forest with all of our senses. In 1982, the National Forest Authorities of Japan suggested advertising Shinrin-yoku to the public and promoting its immune-boosting powers. And today, taking in the forest atmosphere is officially a recognized method of preventing disease and supplementing treatment in the country. The National Institute of Public Health of Japan promotes Shinrin-yoku, universities study it, and hospitals use it as an Rx.
When you breathe in the woods, you are inhaling a cocktail of bioactive substances released by plants. One of these groups of substances is called terpenes. They're usually emitted from leaves, pine needles, tree trunks, and the thick bark of some trees. We absorb these gaseous terpenes partially through our skin, but especially through the lungs. Terpenes also flow out of bushes, herbs, and shrubs among the understory, along with mushrooms, mosses, and ferns, too. Even thin layers of foliage on the forest floor emit them. So, safe to say, if you're outside and can see any sort of tree material, you're getting a dose of terpenes.
While forest medicine is under no circumstances a replacement for conventional medical check-ups, scientific studies have discovered the forest air is like an old friend to our bodies. Some of these terpenes have been found to1 have anti-inflammatory, anti-tumorigenic, and neuroprotective activities, making forest air like a healing elixir we inhale. Even though terpenes come from trees, mushrooms, and herbs that are communicating with one another, our immune system can also decode them. Like other plants, we respond to terpenes by strengthening our body's defenses. Doctors of forest medicine know that anti-cancer terpenes2 have a direct impact on the immune system as well as an indirect impact on the endocrine system. For example, they help us deal with stress by lowering our cortisol levels3.
Forest bathing has also been found to enhance something called natural killer cells4, another defense against diseases like cancer. Those who spend merely one day in the forest will have more natural killer cells in their blood for seven days thereafter. Those who are in the woods for two or three days have elevated levels for another 30 days. It's incredible to think that we get these long-lasting health benefits simply by existing in the woods. We don't have to go on a trail run or rigorous hike (though those things are great too); just breathing and being in communion with trees is enough.
This knowledge totally changed the way I look at nature. Now, when I walk through the woods, I feel like I’m diving into an enormous living organism. I'm becoming a part of it, and we're breathing and communicating together.
Practical ways to make your next trip into the forest even more fulfilling:
1. The content of the anti-cancer terpenes in the forest air changes over the seasons. The highest concentration is in summer, and the lowest is in winter. They increase rapidly in April and May and reach their peak in June and August. Try to go out during these months if you can!
2. You can find the highest concentration of terpenes in the middle of the forest since tree population is the densest there. This dense canopy prevents gaseous terpenes from escaping too. Try to go farther into the woods instead of lingering on the edges when you can.
3. When the air is moist—after rain or during fog, for example—a particularly large amount of healthy terpenes will be swirling around the atmosphere. So if you've ever felt especially great during a walk in the woods after a rain shower, you're not alone!
Who's ready to take a walk in the woods? Check out our 101 guide to forest bathing.
Clemens G. Arvay, MSc, is a biologist and nonfiction writer who centers his work on the relationship between man and nature, focusing on the health-promoting effects of contact with plants, animals, and landscapes. His new book is The Biophilia Effect: A Scientific and Spiritual Exploration of the Healing Bond Between Humans and Nature (Sounds True, February 2018). For more, visit https://www.clemensarvay.com.