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Recharge and Rejuvenate with Forest Bathing

There’s something about being in nature that makes you feel better. Inhaling fresh clean air and the deep aroma of the forest, the recognizable melody of animals and plants of the forest, and the stunning beauty all around unite to ease stress and worry and help you think more clearly. Bathed in the proverbial forest, your mood is enhanced, body rejuvenated, spirit recharged, and energy and vitality restored.

What is forest bathing (forest therapy)?

A decades-old practice in Japan, forest bathing (or shinrin-yoku), literally means to bathe in the atmosphere of the forest using all of your basic senses—sight, touch, hearing, smell, and taste. It involves a profound connection with nature, bridging the gap between us and the natural world. Slowing down and immersing yourself in the natural environment has become an important part of preventative healthcare in Japan. Critics may ridicule this practice as nothing more than a stroll through a forest, but the growing body of evidence suggests that getting outside in nature is food for the mind, emotions, body, and spirit.

People who use essential oils are familiar with the terms terpenes and terpenoids. Inhaling these volatile organic compounds found in all essential oils provides a broad range of biological activities that support human health. Similarly, terpenes and terpenoids emitted by the trees of forests “bathe” us in beneficial volatile organic compounds when walking among nature. These compounds may reach their peak concentration during daylight hours, on clear calm days, from noon to the early afternoon, particularly in forest dominated by conifer trees. (1)

For such a simple health strategy, forest bathing provides huge benefits. Here are some of the benefits science has revealed so far.

Aid cardiovascular health

Your blood pressure is a major indicator of cardiovascular fitness. High blood pressure can damage arteries and increase the risk that they will clog, threatening both your health and quality of life. Japanese researchers studied the effects of walking in a forest on blood pressure. Middle-aged adults who walked in a forest for 90 minutes experienced reduced systolic and diastolic blood pressure as well as reduced stress. (2)

Another study tested the effects of forest bathing on middle-aged men with blood pressure on the high side of normal. The men strolled through the forest, practiced deep breathing, and were allowed periods of time to lie down in the forest. Systolic and diastolic blood pressure, as well as cortisol, all significantly decreased after forest bathing. Moreover, the participants reported improved mood and feeling more relaxed and natural. (3)

A third study evaluating elderly persons with high blood pressure showed that blood pressure was not lowered by forest therapy, but salivary cortisol levels significantly decreased. (4) Quality of life also improved. A reduction in salivary cortisol levels suggests the participants were less stressed. Cortisol plays a role in increased blood pressure. The reduction in cortisol and increased quality of life means that forest bathing may be useful as part of an overall high blood pressure management program.

The cardiovascular benefits of forest bathing aren’t just for the middle-aged or elderly though, research shows that young people can benefit as well. When comparing walking in a forest to urban walking among young adults, researchers found that nervous system activity was balanced towards relaxation, which relaxed the cardiovascular system. (5) Overall, this suggests that forest bathing may support cardiovascular longevity.

Benefits of forest bathing have even been observed in people with chronic heart failure. (6),(7),(8)

Improve emotional and mental health

Most anyone who has walked through a forest or even a fruit orchard can tell you that they felt more relaxed. Interestingly, researchers found that just viewing a kiwifruit orchard image can reduce stress. Middle-aged females were split into two groups. One group viewed a kiwifruit orchard image for 10 minutes while the other group viewed an urban building for the same amount of time. The group that viewed the fruit orchard image experienced increased parasympathetic nervous system activity (a sign of recovery and relaxation), a modest decrease in heart rate, and reported feeling more comfortable and relaxed as well as an improved mood state. (9) Maybe you should plaster your office or another room with nature pictures.

A larger study of almost 500 participants showed that forest bathing significantly reduced hostility, depression, and stress in people who were chronically stressed. (10) Interestingly, the more stressed a person was, the greater the benefits of the forest therapy. Similar findings were reported among people who had depressive tendencies when compared to those who did not. While both groups of people realized physiological and psychological benefits after a day-long session of forest bathing, people with depressive tendencies had more dramatic responses. (11) Mother Nature seems to recognize those who need her loving care the most and delivers extra benefits to them.

Remarkably, other researchers found that forest bathing improved mental health measurements in people being treated for a psychotic illness in in a psychiatric hospital. (12) Patients at the hospital were taking to a local forest covered mainly by conifer trees (Scots Pine, Norway Spruce) and some oak and common beech trees. They were encouraged to walk and participate in other exercises like stretching for 105 minutes. The greatest improvements were seen in confusion and depressive-dejection feelings and a significant decrease in anxiety was observed.

Even shorter walks of 15 minutes in nature can improve mental and emotional health. (13)

Relieve pain and reduce inflammation

Chronic pain can significantly reduce quality of life and take a toll on physical, mental, and emotional health. Adults aged 25 to 49 were taken to a forest filled with pine, oak, and maple trees for two days and participated in various indoor and outdoor activities. At the end of the two days, forest bathing improved both psychological and physical measures. The participants reported less pain and depression and a significant improvement in quality of life. (14) Amazingly, the forest therapy also improved their immune function as indicated by enhanced natural killer cell activity.

Exercising in the forest may provide greater benefits according to one study. The researchers compared the pain-relieving effects of forest bathing in comparison to forest bathing with exercise in people with chronic neck pain. People in the forest bathing with exercise group experienced greater neck pain relief than those in the forest bathing group alone. (15)

Another study found that two-hours of exposure to a forest reduced inflammatory cytokine levels in young adults. (16) Reduced inflammatory cytokines indicates forest bathing can reduce systemic inflammation. The forest intervention also increased antioxidant capacity.

Improve respiratory and immune function

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease characterized by difficulty breathing, cough, wheezing, and excess mucus production. Forest bathing significantly decreased proteins—perforin and granzyme B—released by natural killer cells that are involved in the progression and activity of COPD in elderly individuals with COPD. (17) The therapy also reduced pro-inflammatory cytokine and stress hormone levels and improved overall mood state. Based on the findings, the researchers concluded forest bathing has a positive health effect on elderly people with COPD.

Speaking of natural killer cells, these white blood cells play a major role in the fight against cancer and viruses. Adults who participated in three-day and 2-night forest bathing trips experienced increased natural killer cell activity that lasted for 30 days after completion of the trip. (18) Forest therapy also improved levels of proteins released by natural killer cells that attack viruses and cancerous cells. In contrast, a trip to the city had no effect of natural killer cell numbers or activity. Forest bathing appears to have long-term benefits on immune system function.

Three additional studies noted increased natural killer cell activity and levels of anti-cancer proteins in people of various ages after trips to a forest. (19),(20),(21) So, a monthly trip to the forest may protect you against infections and reduce your risk of cancer.

Conclusion

The existing research is clear. Humans have an intimate connection to nature and immersing yourself in a natural environment has huge human health benefits. If you need a mood reset, want to reduce stress, or improve your physical health, make every effort to inhale the health-promoting aroma of a forest at least once per month.

Diffusing essential oils: Harmful or beneficial to human health?

Hundreds of thousands of people enjoy diffusing essential oils daily to improve mood, relax, and create a more pleasant environment. But, a growing number of consumers are concerned that this practice may be harmful based on widely publicized reports that terpenes found in essential oils may interact with constituents in the atmosphere (carbon dioxide, methane, ozone, etc.) to form toxic oxidation products. Is this concern warranted or just hype from those who don’t believe essential oils have a place in the home?

Evidence suggests that terpenes in essential oils (limonene, alpha-pinene, linalool, etc.) are not harmful by themselves. However, their structure — comprised of one or more carbon to carbon bonds — makes them extremely susceptible to reactions with atmospheric constituents.(1,2) When these reactions occur, toxic oxidation products are produced such as formaldehyde, acetaldehyde, organic acid, and hydrogen peroxide, which are called hydroxyl radicals and secondary organic aerosols (SOAs).(3-6) These oxidation products can be harmful to human health.

Short-term exposure to oxidation products may cause sensory irritation, headache, dizziness, chest pain, and respiratory problems.(7-9) Children, the elderly, people who are obese, diabetics, and people with chronic respiratory disorders are more likely to experience these adverse health effects.

The risk of reactions between terpenes and atmospheric constituents is dependent on temperature and the amount of ozone present indoors. Reactions are more likely to occur in warm seasons when temperatures are higher as opposed to the colder temperatures of cold seasons.(10) In addition, higher levels of ozone provide more atmospheric constituents for essential oil terpenes to react with. Indoor ozone quantities can increase based on the amount of ozone present outdoors or use of certain equipment (laser printers, photocopiers, and some air cleaning units).

Limonene (found in two isometric forms: d-limonene — citrusy scent and found in citrus oils; and l-limonene — piney scent and found in tree oils) is more susceptible to these reactions than other terpenes like linalool. This suggests that essential oils with significant amounts of limonene may require more caution when diffusing, particularly during warm seasons and when the presence of ozone is elevated. To identify some essential oils with high limonene levels see Appendix A of Evidence-Based Essential Oil Therapy.

Synthetic terpenes are often used in cleaning products as scents and solvents. One study determined that the ordinary use of terpene-based cleaning products (typically synthetic limonene, not the limonene naturally found in essential oils) will not produce enough terpene reaction products to exceed safety levels set by regulatory agencies.(11) In other words, use of these cleaning products under normal circumstances is not likely to produce enough oxidation products to be harmful. And this is from an isolated synthetic molecule, which is far more prone to cause adverse effects than a balanced essential oil with all of its natural constituents.

Increased levels of ozone-terpene reaction products have also been observed in spas where essential oils were frequently used during massages and other treatments.(12) This is not surprising considering the amount of essential oils that could be used in a single day in a busy spa. By the end of a day, hundreds of drops of essential oils could have been used during spa treatments. But, remember all chemicals — even water — are dangerous at too high a concentration, and the research thus far suggests that the oxidation of terpenes does not reach levels considered unsafe. In addition, spas often offer other services that produce harmful chemicals like nail care, hair dyes, make-up treatments, and more.

The bottom line is that reasonable diffusing and use of essential oils is not likely to create enough oxidation products to be harmful to human health. The vast benefits of diffusing essential oils far outweigh the minimal risks of producing oxidation products. However, certain populations — children, the elderly, people who are obese, diabetics, and people with chronic respiratory diseases should be more cautious when diffusing essential oils. In addition, it is prudent to take steps to reduce the risk of forming terpene oxidation products.

Here are some tips to reduce the risk of excess formation of terpene oxidation products:

  • set your diffuser to intermittent so it is not constantly diffusing essential oils into the air, but releases them at intervals;
  • add only 3-5 drops of essential oils to your diffuser at one time;
  • diffuse for shorter periods of time (30 to 60 minutes continuously before taking a few hours break);
  • limit diffusion of citrus and tree oils that are high in limonene;
  • make sure the room you diffuse in is well ventilated;

Secondly, here are some tips to reduce ozone in your indoor environment by:

  • avoiding the use of indoor “air cleaners” that emit ozone intentionally (ozone generators) or as a byproduct of their design (ionizers, electrostatic precipitators);
  • making sure rooms with office equipment (laser printers, copiers, etc.) are well ventilated;
  • avoiding the use of oil- and solvent-based paints, degreasers, and lighter fluid;
  • and increasing the number of indoor plants in your home.

(1) Nazroff WW, Weschler CJ. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. Atmos Environ. 2004;38:2841-65.

(2) European Collaborative Action. Urban air, indoor environment and human exposure, report No. 26: Impact of Ozone-initiated Terpene Chemistry on Indoor Air Quality and Human Health. 2007.

(3) Wang B, Lee SC, Ho KF, et al. Characteristics of emissions of air pollutants from burning of incense in temples. Hong Kong Sci Total Environ. 2007;377:52-60.

(4) Waring MS, Wells JR, Siegel JA. Secondary organic aerosol formation from ozone reactions with single terpenoids and terpenoid mixtures. Atmos Environ. 2011;45:4235-42.

(5) Waring MS. Secondary organic aerosol in residences: predicting its fraction of fine particle mass and determinants of formation strength. Indoor Air. 2014;24:376-89.

(6) Pathak RK, Salo K, Emanuelsson EU, et al. Influence of ozone and radical chemistry on limonene organic aerosol production and thermal characteristics. Environ Sci Technol. 2012;46:11660-69.

(7) Nojgaard JK, Christensen KB, Wokoff P. The effect on human eye blink frequency of exposure to limonene oxidation products and methacrolein. Toxicol Lett. 2005;156:241-51.

(8) Wolkoff P, Clausen PA, Wilkins CK, et al. Formation of strong airway irritants in terpene/ozone mixtures. Indoor Air. 2000;10:82-91.

(9) Wolkoff P, Clausen PA, Larsen ST, et al. Airway effects of repeated exposures to ozone-initiated limonene oxidation products as model of indoor air mixtures. Toxicol Lett. 2012;209:166-72.

(10) Geiss O, Giannopoulos G, Tirendi S, et al. The AIRMEX study VOC measurements in public buildings and schools/kindergartens in eleven European cities; Statistical analysis of the data. Atmos Environ. 2011’45:3676-84.

(11) California Air Resources Board and the California Environmental Protection Agency: California Air Resources Board Research Division Indoor Air Chemistry: Cleaning Agents, Ozone and Toxic Air Contaminants. 2006 Apr.

(12) Hsu DJ, Huang HL, Sheu SC. Can Aromatherapy Produce Harmful Indoor Air Pollutants? Environ Engineering Sci. 2011 Oct.