While some of the health benefits are experienced through participating with the forest in a mindful and relaxing way, others are offered directly from the trees.

The trees emit aromatic organic compounds called phytoncides. Translated from Greek and Latin, it means “plant” and “killer.” Phytoncides are part of the tree's immune system, protecting it from pests and pathogens. Because we evolved with trees, these phytoncides protect us too. When we breathe them in through the forest air, they boost our immune system, increasing the number of natural killer cells that attack stressed cells, including virus infected cells as well as boosting anti-cancer proteins. Phytoncides are also responsible for reducing the stress hormone, cortisol, and blood pressure. The longer you are in the forest, the greater the immune boost and the longer the effects. For example, spending three days in the forest can boost your immune system for up to 30 days. The natural aromatherapy of phytoncides is emitted by nearly all plants. You can smell these in conifers, that signature scent that says, “I am pine.”

But it’s not just the trees; breathing in the soil can also reduce stress and make you happy, ask any gardener. The smell of soil microbes, specifically mycobacterium vaccae, found in soil, leaf litter, and compost promotes healthier levels of cytokines, which is linked to higher levels of serotonin, a mood enhancing hormone.

Another boost in health can come from negative ions. Negative ions are odorless, tasteless, and invisible molecules that we inhale in abundance in certain environments. They are most commonly found near moving water, such as, waterfalls or the ocean. They are believed to increase the flow of oxygen to the brain, boosting our mental clarity. They are also believed to increase levels of serotonin, helping to alleviate depression, relieve stress, and boost our daytime energy.

“Grounding,” or “earthing,” is a therapeutic technique that focuses on realigning your electrical energy by reconnecting to the Earth. You can practice earthing by walking barefoot, lying down on the earth, or using conductive mats indoors. Earthing is shown to improve sleep, lower inflammation, and improve blood flow.

In addition to the benefits above, when we are outdoors we also gain the benefits of Vitamin D production through our skin, breathing in fresh air, moving our bodies, and perhaps feelings of awe and wonder, all of which help boost our mood and overall well-being.

The New York Department of Environmental Conservation summed up the benefits:

Exposure to forests boosts our immune system. While we breathe in the fresh air, we breathe in phytoncides, airborne compounds that plants give off to protect themselves from insects. Phytoncides have antibacterial and antifungal qualities which help plants fight disease. When we breathe in these compounds, our bodies respond by increasing the number and activity of a type of white blood cell called natural killer cells or NK. These cells kill tumor- and virus-infected cells in our bodies. In one study, increased NK activity from a 3-day, 2-night forest bathing trip lasted for more than 30 days. Japanese researchers are currently exploring whether exposure to forests can help prevent certain kinds of cancer. (1)

Spending time around trees and looking at trees reduces stress, lowers blood pressure, and improves mood. Numerous studies show that both exercising in forests and simply sitting looking at trees reduce blood pressure as well as the stress-related hormones cortisol and adrenaline. Looking at pictures of trees has a similar, but less dramatic, effect. Studies examining the same activities in urban, unplanted areas showed no reduction of stress-related effects. Using the Profile of Mood States test, researchers found that forest bathing trips significantly decreased the scores for anxiety, depression, anger, confusion, and fatigue. And because stress inhibits the immune system, the stress-reduction benefits of forests are further magnified. (1)

Green spaces in urban areas are just as important as rural forests. About 85% of the US population lives in suburban and urban areas, and may not have access to traditional rural forests. That's O.K. Gardens, parks and street trees make up what is called an urban community forest. These pockets of greenspace are vitally important because they are the sources of our daily access to trees.

Spending time in nature helps you focus. Our lives are busier than ever with jobs, school, and family life. Trying to focus on many activities or even a single thing for long periods of time can mentally drain us, a phenomenon called Directed Attention Fatigue. Spending time in nature, looking at plants, water, birds, and other aspects of nature gives the cognitive portion of our brain a break, allowing us to focus better and renew our ability to be patient.

In children, attention fatigue causes an inability to pay attention and control impulses. The part of the brain affected by attention fatigue (right prefrontal cortex) is also involved in Attention-Deficit/Hyperactivity Disorder (ADHD). Studies show that children who spend time in natural outdoor environments have a reduction in attention fatigue, and children diagnosed with ADHD show a reduction in related symptoms. Researchers are investigating the use of natural outdoor environments to supplement current approaches to managing ADHD. Such an approach has the advantages of being widely accessible, inexpensive, and free of negative side effects.

Patients recover from surgery faster and better when they have a "green" view. Hospital patients may be stressed from a variety of factors, including pain, fear, and disruption of normal routine. Research found that patients with "green" views had shorter postoperative stays, took fewer painkillers, and had slightly fewer postsurgical complications compared to those who had no view or a view of a cement wall.

Department of Environmental Conservation