Health Impacts of Nature Immersion

 “Nature itself is the best physician.” -Hippocrates


In the past few decades, there has been a massive amount of research done on the health impacts of spending time in nature. While theAssociation of Nature and Forest Therapy teaches a technique that also draws on unquantifiable benefits, we value the empirically demonstrated health benefits of the practice and of wider nature connection research. It is important for guides to understand and be able to explain the grounding health science literature for three main reasons: 

  1. Having this knowledge allows guides to communicate the benefits of the practice to a wider audience. Audiences will be attracted to the practice of Forest Therapy for different reasons, one of whichis to seek the quantifiable physical and mental health benefits of guided forest immersions. 
  2. Having this knowledge allows guides to confidently speak to the press, who invariably ask about this topic.  
  3. Having this knowledge allows guides to understand the connection between Forest Therapy and the Japanese practice of Shinrin-yoku

When discussing the health impacts of nature immersion, it often serves to begin with a simple question, “Try to remember when you spent an extended period of time in nature. Maybe it was a camping trip or a long hike. Do you remember how you felt during that time?” 

Most people, even those without any knowledge of health science, will remember feeling healthy in some way. Then we might ask, “What are some of the things you remember?” The answers to this question mostly fall into three categories: 

  • Physiological Health Impacts. These might include more energy, better sleep, enhanced immunity, healthy digestion,reduced inflammation, lowered blood pressure, etc. 
  • Mental Health Impacts. These might include increased focus, enhanced creativity, less stress, enhanced memory,improved mood, less anxiety, relaxation, etc. 
  • Emotional and Psycho-Spiritual Health Impacts.These might include people feeling more connected, more alive, more present, as well as having experiences characterized by joy, transformation, rest,forgiveness, grief, self-acceptance, love, reconciliation, insight, dreams,awe, perspective, purpose, empowerment, empathy, integration, release,wholeness, etc.  

It is beyond the scope of this document to explore all these ways that nature improves human health, especially as researchers continue to discover new and exciting evidence. Later in this manual, we’ll explore more of the ways in which Forest Therapy might lead to some of the effects described in the third category, which generally fall outside of a biomedical explanation.

For now, this chapter aims to explore three health science topics as a way to help guides understand the connection between the health benefits of nature immersion and the pedagogical approaches described in this manual. For a more in-depth base of research, there is a link in the ANFT MembershipPortal to a wide array of scientific literature, including studies that cite more specific data than is addressed in this manual.  

The Health Science of Relaxation: Forest Therapy and the Human Nervous System 

Human beings have evolved a nervous system that allows them to manage sudden bouts of stress with the aid of the sympathetic nervous system. The sympathetic nervous system rapidly changes the biology of the human body when the body perceives danger and puts the body into what is known as“fight, flight or freeze” mode. If a mountain lion charges a person, that person’s body will automatically trigger one of these modes, which does things such as increasing heart rate, blood pressure, and respiration, and decreasing memory capacity, learning, and digestion. The stress modes prioritize survival above all else. When a mountain lion chases a person, that person’s brain doesn’t care about learning new skills or digesting food, it just wants to getaway as fast as possible. 

There is a fourth stress response which has been recently added and is known as “fawn”, or the “please” response, and is focused on adapting to avoid confrontation or danger.

The biological changes in the body in response to danger are triggered by hormones such as adrenaline and cortisol, which flood the body when the sympathetic nervous system is activated. Since the sympathetic nervous system is part of the autonomic nervous system, humans have no direct control over it (compared to actions like walking or talking, which are part of the somatic nervous system and that we do control). This means, people don’t control when they get triggered into fight or flight.  

Once danger is escaped, the body then activates the parasympathetic nervous system, whose function is known as “rest and digest.”The person who escaped the mountain lion and returns to a sense of being safe will reflexively begin to redirect energy to digestion, learning, memory,resting, and rebuilding muscle tissue == the processes that support healing.This is all done without  our conscious action.

One of the critical problems of the 21st century is that our bodies are designed for the 2nd century but our cultures have rapidly evolved.Today, people’s bodies activate the sympathetic nervous system not because a wild animal is chasing, but because they are connected to an incredible amount of information that is, highly stressful, and they are surrounded by stimuli –such as traffic, congested cities and loud noises -- which may be perceived as threatening to their safety

Whether it’s the threat of nuclear war, natural disasters, climate change, terrorism, economic destabilization, or any other array of calamities, people get stressed all the time because they get notifications on their phones that their bodies interpret in much the same way as the body would if a mountain lion were chasing it. The body uses up stress hormones such as adrenaline and cortisol only through physical exercise (like running away from the lion), and if there is no physical release and stress hormones linger in the body, they can begin to have toxic impact.

Thus, modern stress triggers are doubly dangerous as people become more sedentary and fail to get rid of the stress hormones. To make matters worse, because the body craves chemical equilibrium, humans can become accustomed to and even addicted to stress. When this happens, people may act in ways that promote the constant triggering of the sympathetic nervous system.Stress addiction is linked to issues such as anxiety, depression, poor digestion, headaches, insomnia, heart disease, weight gain, and attention and memory loss. 

One of the reasons Forest Therapy is an innovative modern health solution is that it draws on nature’s ability to calm us down and activate the parasympathetic nervous system. Research has shown that the parasympathetic nervous system can be activated through mindfulness activities,such as focused breathing. Forest Therapy falls into this category as well.There is an incredible amount of research demonstrating that simply seeing the colors green and blue can ease our bodies toward relaxation. When we activate the senses of the body, we are shifting attention away from the cycle of thoughts that can often trigger the stress response, and moving our focus toward states of rest and relaxation that promote parasympathetic response.  

Often, modern people address the pandemic of stress by numbing themselves with drugs and alcohol, but this is not a biologically healthy solution. Activating the parasympathetic nervous system is our body’s innate mechanism for health and wellbeing. When we activate this rest and digest mode, our bodies are healing themselves.

Many modern people complain of chronic exhaustion, which researchers believe may be due in part to the fact that people are not absorbing nutrients and energy from the food they eat due to the ineffective parasympathetic response. It does not matter if the food is healthy if the body is not capable of digesting and absorbing those nutrients. This is just one of many health outcomes that rely on the power of the parasympathetic nervous system. Beyond digestion, the parasympathetic nervous system promotes health of the kidneys, lungs, heart, intestines, and reproductive organs. So, while it’s good to have the sympathetic nervous system when a mountain lion rushes, daily health is really a function of the parasympathetic nervous system, which is why it is important for people to slow down, relax, and breathe. Forest Therapy helps us do this. 

Forest Bathing, Immunity, and Phytoncides 

The human body defends itself against infectious organisms and other invaders through the immune system. One important weapon in the immune system’s arsenal are white blood cells. White blood cells come in two varieties and each serve distinct functions. The first type, called phagocytes,attack and kill invading bacterial organisms. The second type, called lymphocytes, help the body remember and recognize previously encountered invaders so that they can be more easily defeated in future instances of infection.  

There are two types of lymphocytes: B-cells and T-cells.B-lymphocytes identify and locate infected cells and T-lymphocytes eliminate them. T-cells are the kind that kill cells infected by viruses and cancerous cells.  


There are special white blood cells called Natural Killer(NK) cells. NK-cells are like the body’s first responders. They can notice cancerous and infected cells before other white blood cells have been activated.  

When people go into the Forest, something quite incredible happens. Their bodies produce more NK-cells.

Trees are biological organisms that have their own ways of defending themselves from attacking organisms. One of the ways trees protect themselves is by diffusing a special class of chemicals into the air called phytoncides. Phytoncides are chemically similar to the essential oils produced by plants and are active substances that are anti-bacterial, anti- fungal,anti-viral and prevent the plants from rotting. When a tree is threatened by an attacking organism, such as a fungus, the tree responds by showering itself with these phytoncides, which then seek out and destroy the fungus.  

When humans inhale phytoncides or absorb them through the skin, it prompts the human body to produce NK cells. For this reason, Japanese researchers named their practice of forest medicine “Forest Bathing (Shinrin-yoku)” because when people are in the Forest, they are bathing in the phytoncide-rich atmosphere of the Forest—a sort of “natural aromatherapy.” 

Phytoncides released from trees also decrease the production of stress hormones, and have  a calming effect on humans. It is well known that stress inhibits immune function, and that a properly functioning immune system plays an important role in maintaining human health.  So, forest environments may boost the human immune system by reducing stress and increasing immune-cell function.. For these reasons, Forest Therapy can be viewed as an effective strategy to maintain and boost immune strength in human beings. 

Attention Restoration Theory and Forest Therapy 

There are many studies that suggest that time spent in nature has positive effects on attention, cognitive performance, emotions,mood, and behavior, although it is important to point out that many of these studies need further academic support to move beyond the realm of theory. One of these studies is Attention Restoration Theory (ART) as proposed by Rachel andStephen Kaplan.  

The Kaplans theorize that there are four cognitive states on the pathway toward cognitive restoration: 

1)   Clearer head, or concentration. 

2)   Mental fatigue recovery.

3)   Soft fascination, or interest. 

4)   Reflection and restoration. 

In the first and second stages, people set aside the thoughts, worries, and concerns of their everyday lives and allow their minds to rest. In Forest Therapy, this is accomplished through Pleasures of Presence and What’s in Motion, as the guide shifts participants’ awareness away from thinking and into their senses and bodies. 

The third stage allows people to be gently distracted and engage in a low stimulation activity. This creates a quiet internal space for relaxation. In Forest Therapy, this occurs in the liminal phase of the walk. 

The final stage is reached once a person has spent a prolonged amount of time in a natural, restorative environment. Once here, they are able to relax, restore their attention and reflect on their life. This is accomplished in Forest Therapy as part of the threshold of incorporation  and the lingering after tea ceremony.