Defining biophilia

I have often explained that essential oils help to re-establish the subtle and profound spiritual connections that we have long had with nature. Fischer-Rizzi beautifully explains that getting to know these heavenly scents is like falling in love. They will touch your heart and make you more keenly aware of the beauty around you, and they will open the door to your soul.1

E.O. Wilson coined the term biophilia in 1984, referring to our innate and natural affinity for nature. It is suggested that we have a biological, emotional and spiritual need to connect with nature and that we are genetically determined to love the natural world.2

Shinrin-yoku – forest bathing

Many cultures have long been aware of the unique relationship we have with nature. For example, in Japanese, shinrin-yoku is defined as ‘forest bathing’ or ‘taking in the forest atmosphere’.3,4

Li explains that shinrin-yoku means bathing in the forest atmosphere, or taking in the forest through all our senses. It does not imply exercising, hiking or jogging in the forest; it simply means being in nature and connecting with it with all our senses.5

Many Japanese studies have reported that natural environments provide better emotional, physiological and restorative effects, and improved work performance than an urban environment. Some of the positive health outcomes include lowered blood pressure, reduced muscle tension and increased brain wave activity in the alpha frequency.3,4,5

Researchers examining the effects of forest bathing found significantly decreased urine adrenaline and noradrenaline concentrations in both male and female subjects. Other studies have reported that forest bathing reduced saliva cortisol levels, prefrontal cerebral activity and blood pressure in humans, as well as stabilising autonomic nervous system activity.3

One study found that forest bathing increased Natural Killer (NK) activity, which in turn increased the levels of intracellular anticancer proteins such as perforin, GRN and GrA/B. Li suggests that regular forest bathing may have a preventative effect on cancer generation and development.3

Another study stated that two 2-hour forest walks on consecutive days increased the number and activity of anticancer NK cells by 50 and 56% respectively, and the activity remained significantly high even a month after returning to urban life – 23% higher than before the walks. It was also found that extended time in the forest decreased inflammatory cytokines implicated in chronic disease by roughly one-half. Urban walks had no such effect.6


Li introduces us to the philosophy and science of shinrin-yoku in his beautifully written and illustrated book Forest Bathing. Li attributes the therapeutic benefit of forests to phytoncides. He explains that the forest is full of phytoncides.5

Guess what these phytoncides are? They are the essential oils that can be found in the leaves of the forest trees.

The term ‘phyton’ is Greek for ‘plant’ and ‘cide’ is ‘to kill’. Li explains that phytoncides are also part of the communication pathway between trees. The warmer the forest is, the higher the concentration of phytoncides in the air. The concentration is highest at temperatures of around 30˚C.5

The chemical composition of phytoncides varies from tree to tree. The most common scent in Japan is from the Japanese hinoki cypress, Chamaecyparis obtusa.  The most common chemical components found in phytoncides include d-limonene, α-pinene, β-pinene and camphene.5

Li’s research has shown that exposure to phytoncides has:5

  • significantly increased the number of NK activity, enhancing the activity of anticancer proteins
  • significantly decreased the levels of stress hormones
  • increased the hours of sleep
  • decreased anxiety, aggression, fatigue and mental confusion
  • stimulated a pleasant mood
  • significantly lowered blood pressure
  • suppressed sympathetic nervous system activity and increased parasympathetic nervous activity.

All evergreens such as pine trees, cedars, spruces and conifers are large producers of phytoncides. It is, therefore, not surprising that Li states we can achieve similar results by diffusing essential oils.5

The phytoncide compounds released from Cryptomeria japonica (Japanese cedar) were identified as α-pinene (19.35%), β-myrcene (16.98%), d-limonene (15.21%) and γ-muurolene (7.42%). In one study the neuropharmacological activity of the essential oil from the leaves of C. japonica was evaluated and found to prolong the sleeping phase of mice in the pentobarbital-induced sleeping time model. Some of the compounds were found to reduce anxiety and provide relaxing and stress-relieving effects on mice. It was suggested that further studies of the effects of phytoncides on humans are worthwhile.7

There is another study that found that the smell of Japanese cedar chips significantly decreased systolic blood pressure within 40 to 60 seconds following the commencement of inhalation. The prefrontal area also exhibited a rapid decrease in brain wave activity with the inhalation of the smell of cedar chips. Another study found that the scent of hiba (Thujopsis dolabrata) significantly mitigated depression and anxiety in chronic haemodialysis patients.8

Other studies have found that DHEA levels were higher in individuals after walks in the forest but not in an urban environment. DHEA has cardioprotective, anti-obesity, and antidiabetic properties. It was also reported that walks in the forest, but not walks in urban areas, reduced inflammatory cytokines.6

Arvay states that the many conifers such as cedar, cypress, pine, Scots pine, spruce and fir are able to emit healthy terpenes. Deciduous trees such as beech, oak, birch and hazel also emit large amounts of terpenes that strengthen our immune system.9

The role of microbes

Li states that when we walk in the forest we breathe in common and harmless bacteria Mycobacterium vaccae that is found in the soil.5

Mary O’Brien, an oncologist at Royal Marsden Hospital in London, discovered that lung cancer patients inoculated with a strain of M. vaccae demonstrated an improvement in emotional health, vitality and even cognitive function. It has been suggested that the body’s immune response to the bacterium causes the brain to produce serotonin. A lack of serotonin is often linked with depression.10

Another study examining stress responses of mice found that those mice injected with M. vaccae exhibited lower levels of stress. It has been suggested that we may encounter these organisms while we are outdoors in contact with the soil and that these microorganisms may help decrease anxiety and improve the ability to learn new tasks.10

This has been confirmed by other studies which state that ingestion of M. vaccae reduced anxiety-related behaviours. It was concluded that the behavioural responses to M. vaccae may be associated with the coevolution of mammalian neuro-immunological systems and ambient microbes.11

Images of nature

Kuo suggests that the sights and sounds of nature are able to reduce sympathetic nervous activity and increase parasympathetic activity.6

Studies found that just looking at natural scenes can promote better health outcomes. For example, one study reported that surgical patients assigned to rooms with windows overlooking natural scenery with trees had shorter postoperative hospital stays, received fewer negative comments in nurses’ notes and had to take less potent analgesics than those in similar rooms with windows facing a brick wall.4

Forest versus urban environment

One study compared the emotional, restorative and revitalising effects of short-term walking in the forest compared to downtown urban areas. The results confirmed that a 15-minute walk in either environment helped to lower tension and anxiety, depression and confusion. However, vigour was significantly higher in the forest environment compared to the urban environment. It was concluded that forest bathing:4

  • improved mood
  • heightened positive affect
  • induced a feeling of subjective restoration
  • induced a feeling of subjective vitality.

Three psychological effects of exposure to nature have been reported:6

  • experiences of awe
  • enhanced vitality
  • attention restoration.

It was suggested that experiences of awe are associated with healthier, lower levels of inflammatory cytokines. Enhanced vitality predicts resistance to infection and lowered risk of mortality and attention restoration may help reduce risky health behaviours such as smoking, overeating and drug or alcohol abuse.6

Central pathways linking nature and health

Kuo attempted to identify the main plausible central pathway linking nature and health. Twenty-one pathways were identified including environmental factors, physiological and psychological states and behaviours or conditions. Kuo states that time spent in and around tree-lined streets, gardens, parks and forested and agricultural lands is consistently linked to objective, long-term health outcomes.6

Kuo states that the less green a person’s surroundings, the higher their risk of morbidity and mortality – even when controlling for socioeconomic status and other confounding variables. It is suggested that there are multiple pathways all operating together to enhance health outcomes. Exposure to phytoncides, exposure to Mycobacteria vaccae, increased adiponectin, stronger social ties, better sleep and enhanced immune function could all be mechanisms by which contact with nature promotes health.6

The need for green spaces in urban environments

Kuo suggests that green spaces should be designed within urban environments to induce feelings of deep relaxation, awe and vitality. Providing green spaces in high-risk urban environments might actually be a powerful public health intervention and help address persisting health inequalities.6

In another study, city residents with more green spaces in their residential environments reported better psychological and physical health outcomes than people from residential areas with fewer greener spaces. It was suggested that the possible mechanisms linking contact with nature to improved health outcomes include:12

  • improvement in micro-climatic conditions (e.g. air quality)
  • stimulation of physical activity (e.g. exercise)
  • facilitation of social cohesion
  • restoration of mental fatigue.

The mechanisms of the nature-health relationship are still not fully understood and not conclusively backed up by empirical research.12 However, it has also been concluded that it is important to create green and recreational spaces within urban landscapes. The importance of physical activity for human wellbeing, irrespective of stressor levels, was also mentioned.12

Another study showed that people who made long visits to green spaces had lower rates of depression and blood pressure, and those who visited more frequently had greater social cohesion. It was found that visits to an outdoor green space for 30 minutes or more in a week could reduce the prevalence of depression or high blood pressure by up to 7% and 9% respectively.13

The need for more studies

A systemic review of studies examining the relationship between nature and human health did not find convincing evidence of the benefits of forest therapy due to a lack of high-quality studies. However, the authors of this review noted that the potential impact of nature in the form of forest therapy should not be disregarded.14

It also appeared likely that the therapeutic benefits of forest therapy are multi-factorial, involving the green scenery, fresh air, sunlight, clean water, rocks, soil, soothing sounds of streams, waterfalls, birds and the natural aroma of trees, plants and flowers.14

Advice on forest bathing

Li provides us with some practical advice for the practice of forest bathing. He suggests that we should first find the right location. He explains we should find a place where we feel comfortable, somewhere that will fill your heart with joy. He insists that we leave our phone and camera behind! He explains the key to unlocking the healing benefits of the forest is to use all five senses. Let nature enter through your ears, eyes, nose, mouth, hands and feet. He recommends:5

  • Listen to the birds singing and the breeze rustling in the leaves of the trees.
  • Observe the different shades of green leaves and the sunlight filtering through the branches.
  • Smell the fragrance of the forest and natural scent of the phytoncides.
  • Taste the freshness of the air as you take deep breaths.
  • Feel the trunk of a tree, dip your toes and hands into the stream. Lie on the forest floor.

Arvay also provides us with the following information:9

  • The phytoncides are highest in summer and lowest in winter.
  • The denser the forest canopy, the higher the concentration of phytoncides.
  • Whenever the air is moist, after rain, or during fog, there will also be a higher percentage of phytoncides in the forest air.

Using essential oils

There will be times when we cannot get outside for forest bathing. Li suggests that we should then bring the scent of the outdoors indoors by diffusing essential oils extracted from the trees that are found in the forest.5

All the conifer essential oils such as fir, hiba, hinoki, spruce and pine are rich in phytoncides. These conifer oils will remind you of the tranquillity associated with the forest and you are very likely to receive some of the benefits of forest bathing by diffusing the oils.5

Highly recommended reading

Li Q. Forest bathing – how trees can help you find health and happiness.  Viking, New York, 2018.

Arvay CG. The biophilia effect – a scientific exploration of the healing bond between humans and nature.  Sounds True, Boulder, 2018.

Louv R. The nature principle. Algonquin Books, Chapel Hill, 2011.

Williams F. The nature fix – why nature makes us happier, healthier, and more creative. WW Norton & Company, New York, 2017.


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