Have you ever been encompassed entirely by trees, taken a deep breath of crisp forest air and felt a calm zen? If you’ve ever wondered what makes the air so fresh, why the trees make you feel serene (and why all air can’t be that crispy), then you’re in the right place. It’s largely due to terpenes.
Terpenes are naturally occurring chemicals found all throughout the world, emitting a spectrum of distinct scents. Currently, approximately 55,000 terpenes have been identified. A wide and diverse array of organisms produce terpenes including conifers, flowers, insects, marine algae, and sea slugs, among many others. Plants and trees emit these compounds for a myriad of different purposes, while we reap their benefit by interacting with them.
So, what exactly are the terpenes you’re breathing in while you walk through the forest preserve? Some of the most beneficial and prominent terpenes found in forest air are outlined below.A-Pinene
It’s in the name. The crisp scent of a coniferous forest after the rain or the scent of pine cones crackling in a fireplace are both richly infused with a-pinene. Additionally, this terpene provides a signature woodsy overtone found in eucalyptus, juniper, and frankincense essential oils. Pinene is an essential in any forest or wood scented product if you'd like to recreate that serene zen you experience exclusively in the woods.
In clinical studies, alpha-pinene has been noted for its anti-inflammatory benefits. By suppressing the activation of proteins, a-pinene inhibited the inflammatory response in white blood cells. Though the test subjects were mice, anti-inflammatory activity is a signature characteristic of essential oils containing a-pinene.Borneol
Highly-valued in the perfume industry, borneol is partially responsible for the minty camphor-like aroma found abundantly in forest air. Essential oils high in borneol have been valued for their cooling sensation and capacity to reduce swelling. In the forest, borneol is produced by shrubs like mugwort, marjoram, and sage.
Much like a-pinene, borneol is a potent anti-inflammatory. For example, a set of lab rats with induced-lung injuries showed significantly reduced signs of pulmonary inflammation after a small treatment with borneolLinalool
Among the most prolific (and best smelling!) terpenes found throughout forests is linalool. Some may recognize this ingredient commonly in home fragrances, detergents, and cleaning products. Linalool smells a little floral and a bit like mint and pine, but overall it smells fresh and clean. While the best product is extracted from plants, this fragrance is often created synthetically for use in commercial cleaning products or detergents.
When natural linalool is inhaled, it has a cooling and soothing effect on the lungs and bronchial tubes. A study performed at the Harbin Medical University Cancer Hospital in China showed that inhaling linalool relieved the inflammation generally caused by smoking cigarettes. Because of this, linalool may be a potential candidate for maintaining healthy respiratory function.Limonene
Nothing smells “lemony fresh” without an explosion of the terpene limonene. As the name implies, limonene is the sharp and bright fragrance most noted when peeling an orange or slicing open a lemon. Limonene is an excellent disinfectant, but it is most valued for its impressive mood-boosting properties.B-Caryophyllene
Perhaps most noted for its abundance in cannabis, beta-caryophyllene (BCP) is also found in copaiba, cinnamon, ylang-ylang, among other trees and shrubs. The fragrance and flavor of this terpene were well-established before anyone knew that it was also a cannabinoid.
Cannabinoids can interface directly with the body’s endocannabinoid system, which regulates immune function, pain reception, and inflammatory activities, among many other processes. BCP, in particular, activates the CB2 receptors and therefore has none of the psychoactive properties associated with other cannabinoids, making it a cannabinoid with extensive pharmaceutical potential.
Experimental studies have suggested BCP promotes heart health, acts as an antioxidant, relieves inflammation, and maintains a healthy immune system function.Myrcene
Noted for its pungent aroma, myrcene is another terpene found in Cannabis sativa. This terpene plays an important role in the interaction between cannabinoids and the endocannabinoid system. Myrcene is abundant in Vepris macrophylla an evergreen tree found in the subhumid forests of Madagascar, and local cultures have been aware of the curative properties of this tree for a long time.Cymene
With a pleasant smell vaguely similar to licorice, cymene is the terpene that makes anise, cumin, and eucalyptus aromatic and pharmaceutically beneficial. Cymene exists in various forms in different plants—p-cymene is the most abundant of all and the one with the most classified benefits.Sabinene
Forests featuring the Norway spruce and holm oak as well as many members of their family will have higher levels of sabinene than most. Sabinene also lends its fragrant properties to bergamot, nutmeg, and several berries. Essential oils high in sabinene have a place of importance in the perfume industry.
In the pharmaceutical world, sabinene also maintains a position of esteem. As one of the most potent antioxidants in the natural world, sabinene has been the subject of multiple studies. The scientific community has shown that this terpene contains antifungal, anti-inflammatory, and antioxidant properties.Camphor
One of the first plants cultivated for medicinal purposes, camphor was originally collected from the camphor laurel tree and valued for its highly pungent aroma. Camphor comes from a family of evergreen trees known for their aromatic qualities. It can be sourced from several plants, and each will produce a slightly different chemical composition and aromatic profile.
Since it was first discovered a few thousand years ago, camphor has been applied to treating conditions of the respiratory system. Simply crushing the leaves of the tree and inhaling the terpenes released provided a range of health benefits in the past. However, modern refining and extraction methods increase the qualities of this terpene and present it in a variety of essential oils, balms, and decongestants.Consider experimenting with and mixing these terpenes into a candle or room spray if you'd like to have a forest-y smelling room while also feeling the calming effects of woods. If you'd like to know more about a specific terpene isolate, check them here!
Why Do Trees Emit Terpenes?
There are a number of reasons why a tree, or entire forest would produce these chemicals. In some instances - they are highly stressed, in other instances they are changing the climate around them in order to generate rain and/or humidity for the benefit.
Odoriferous leaves, bark, and even roots are often rich in terpenes and terpenoids. Though some scents work to attract pollinators, others are defensive, meant to deter pests and attract pests’ predators. Eucalyptus, sage, and mint are a few examples of defensively-scented terpenoid producers. Terpene production increases dramatically in heat, suggesting that terpenes play a role in temperature regulation in forests.
Abiotic Stress and Terpenes
Typically, conifers release terpenes when they are stressed. Many types of environmental stress can create unfavorable conditions for plants. Both primary and secondary metabolism could be affected by stress factors. These include drought, air and soil pollution, high or low temperatures, high light intensity, salinity and mechanical damage (Bartwal et al., 2013).
The defense mechanisms of plants may either be present constitutively or induced by stress factors. The terpene-related defenses undoubtedly contributed to the evolutionary success of conifer trees (Celedon and Bohlmann, 2019). One of the most typical defense mechanisms in conifers is related to oleoresin, which is a complex, fragrant mixture of volatile and non-volatile terpenoids (monoterpenoids, diterpenoids in almost equal amounts and slightly less sesquiterpenoids) (Keeling and Bohlmann, 2006). Equally important is the oleoresin role in chemo-ecological interactions with co-evolved insects, e.g. bark beetles. Oleoresin terpenes favor host identification and host-herbivore interaction, since they can serve as pheromone precursors (Celedon and Bohlmann, 2019). In Pinus sylvestris and Picea abies, which are the most abundant conifer trees of the moderate climate zone, constitutive resin, known as primary resin, is produced in considerable amounts due to physiological processes, while synthesis of secondary resin is a result of wounding stress (Turtola, 2005).
Winemakers like to say that “grape vines must suffer to make good wine.” Hot days and bitterly cold nights are stressful on the plant and create volatile compounds known as proanthocyanidins. These volatiles, like terpenes, are flavonoids which provide the flavor, and are much more expressed by the plant and abundant in presence when the plant is stressed. All of this to say, there is a direct relationship between the plant’s stress and our satisfaction. The more the plant thinks it is going to die or the closer the plant actually comes to death, the stronger the scent, the more abundant the flavor, and the higher the concentration of terpenes. Thus, the more physiological benefit we receive from these plants. There’s poetic beauty in our relationship with these plants. It’s a yin yang. The greater suffering in the plant, the greater the benefit we receive upon consumption.
Terpenes and Cloud Seeding
Trees use terpenes for their advantage in another fascinating way. When conifers have not received enough water, and when the conditions are right, they will emit terpenes to manipulate their environment and bring themselves rain. Clouds, composed of water vapor, condense around aerosols, and researchers have found that ozone located in the upper atmosphere attaches to molecules of alpha-pinene, a terpene released by pine trees. These highly-ozonated molecules stick together to form heavier particles and serve as an aerosol base for clouds to form to both block sunlight and produce rain.6 While humanity has been trying to control and modify the climate for as long as we’ve existed through ceremonial dances, prehistoric sacrifices, and decades of research, trees have been doing so all along.
The most recent CLOUD experiment, a collaboration between around 80 scientists at the CERN particle physics lab near Geneva vastly increased our understanding of what was in the atmosphere before humans began adding pollution - and what it may be like again in the future. Most cloud droplets need tiny airborne particles to act as ‘seeds’ for their formation and growth. Terpenes emitted from these trees are a viable seed upon which a cloud can generate upon. If a cloud has more of these seeds, it will appear brighter and reflect away more sunlight from the Earth’s surface. This in turn cools the Earth and our climate. Therefore, understanding the number and size of terpenes, among other seeds, in the atmosphere is vital to predicting not only how bright and reflective the planet’s clouds are, but what global temperatures will be.
The discovery that organisms use terpenes to influence their world has huge implications regarding the importance of terpenes in the environment and the role they play in controlling weather. Since one of terpene’s functions is to spur cloud formation, this discovery, adds another two layers to the already well-understood problems associated with cutting down vast swaths of forestry in the process of industrialization. Rising temperatures has an immense number of effects and implications, ranging from rising sea levels, increased droughts and heat waves, to intensified tropical storms.
Since isoprene and other terpenes play a significant role in cloud formation, deforestation has an even bigger impact on the environment than previously thought and the production of terpenes may be integral in slowing the rising temperatures leading to climate change. One is obvious: clouds provide shade, reflecting a broad spectrum of sunlight thanks to their white color. The second, less obvious effect is the greenhouse action of H2O. If a reduction in atmospheric terpenes caused by deforestation does significantly inhibit cloud formation, water vapor that would otherwise form shady clouds instead remain as heat-trapping ambient humidity—unable to condense in the absence of aerosols. Without an abundance of terpene-emitting trees and plants in our environment, a slew of environmental and ecological issues arise.
When To Forest Bathe
Forest bathing is the act of being immersed in nature, surrounded by trees or other greenery. Sometimes called 'shinrin-yoku,' it is simply being in nature, connecting with it through our senses of sight, hearing, taste, smell and touch. Shinrin-yoku is like a bridge. By opening our senses, it bridges the gap between us and the natural world.
The profile of terpenes in many conifer trees may fluctuate depending on the time of day. The study taken in the Landes forest in France (Riba et al., 1987) showed that the atmospheric concentrations of α-pinene and β-pinene emitted by Pinus pinaster trees demonstrated a very wide variation between day and night. In the night the amount of emitted terpenes was about four to eight times greater than during the day. Since it is recognized that the usual plant terpene emission is higher in the day than at night, the above result suggests that the final concentration of terpenes in the air is influenced by additional factors, such as daytime photochemical reactivity or atmospheric dispersion.
Sunlight typically burns away many terpenes, as they are Volatile Organic Compounds (VOC’s). So, consider going for a walk, run, or forest bathing session right before sunrise, and you will experience the most of these life-enhancing terpenes.
Higher amounts of terpenes are released by trees in warmer weather, where they may function as a natural mechanism of cloud seeding. The clouds reflect sunlight, allowing the forest temperature to regulate the temperature to their liking.
The idea of relaxing while walking through a forest—have collected extensive lists of the physical and psychological benefits from that these experiences can bring. Part of these benefits come from the sensory stimuli found in forests, especially when it comes to how compounds in forest air interact with the sense of smell.
An important aspect of Forest Therapy involves breathing in the air in a wooded atmosphere. The air in the woods is rich in naturally-occurring compounds produced by trees for a variety of purposes essential to the long-term survival of the forest.
Trees and plants produce over 40,000 different types of known terpenes, and each one has a special function. These organic compounds also have important applications in pharmacology and have been collected and applied in some of the earliest types of medicine.
A deep inhalation of the forest atmosphere floods the lungs with a variety of terpenes that have the potential to address different aspects of human health. One of the top benefits these compounds can provide is soothing the limbic system and balancing hormone levels. Then, individual terpenes can function as anti-inflammatories, antibacterials, analgesics, and many other curative, therapeutic, or preventive agents.
Many studies have shed light on an extensive selection of benefits for mind and body that the terpenes in forest air provide. Much like aromatherapy, the high concentrations of organic compounds present in forest air introduce their benefits through the tissues of the lungs and bronchial tubes as well as the membranes of the olfactory epithelium.
Go smell some terpenes for yourself!
Can’t escape to the woods? Poke your nose in the nearest pine tree and breathe those terpenes in. Then, go about your business, a little calmer, a little refreshed.
Or bring the woods to you! Buy some plants for your place, plant a tree, or drive to the nearest arboretum. Breathing in fresh, pure air can often be the reset needed in many people's busy, stressful life.
What's your favorite forest-y terpene or scent? If you have a signature scent combination let us know below!
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