Terpene Deficiency & Paleo Air: The Science Behind What Modern Life Ta

By Eric Fishman, M.D., Founder, MONQ

Here is a number worth sitting with: the average American spends approximately 90 percent of their life indoors. Offices, homes, cars, gyms, shopping centers. For most of human history, this would have been unrecognizable. For nearly all of the 300,000 years that Homo sapiens has existed as a species, and for the millions of years of hominid evolution that preceded us, our ancestors lived immersed in the natural world. They moved through forests and grasslands, slept under open skies, and breathed air that was rich with thousands of volatile compounds produced by the plants around them.

That air was not simply oxygen and nitrogen. It was a complex, living chemistry. And our biology evolved to expect it.

The question I have spent years thinking about is this: what happens to the human body when that chemistry disappears? When the air we breathe is filtered, recirculated, and stripped of the botanical compounds that our nervous systems, immune systems, and endocrine systems were shaped by over geological time?

I believe the answer has a name. Two names, actually. The first is Paleo Air: a term I coined to describe the terpene-rich atmospheric environment that humans evolved in, now largely absent from modern life. The second is Terpene Deficiency: my working framework for understanding a class of non-specific wellness challenges that may arise, at least in part, from the chronic absence of these compounds.

Neither of these is a diagnosis. Neither is a product pitch. They are conceptual tools for thinking more clearly about a real phenomenon: the growing mismatch between the environment our biology was built for and the environment we actually inhabit.

This article is an attempt to lay out the science as clearly as I can, to give these ideas the grounding they deserve, and to make the case that the air we breathe is worth paying far more attention to than we currently do.

Part One: Plants Are Not Just Scenery

Secondary Metabolites and the Chemistry of Life

Most people think of plants in functional terms: they produce oxygen, they provide food, they look pleasant. What most people do not know is that plants also produce thousands of chemical compounds that serve none of those obvious purposes. These are called secondary metabolites: molecules that play no direct role in the plant's own photosynthesis, reproduction, or growth, yet are produced in enormous variety and quantity.

Why would a plant invest energy in producing compounds that do not appear to benefit it? For decades, biologists puzzled over this question. The answer, it turns out, is that secondary metabolites are the language through which plants communicate with, defend against, and cooperate with the other organisms around them: insects, fungi, bacteria, mammals, and yes, humans.

Plant secondary metabolites fall broadly into three chemical classes: phenolics (including flavonoids and tannins), nitrogen-containing compounds (including alkaloids, glucosinolates, and amino acid derivatives), and terpenes. Each class contains hundreds to thousands of distinct molecules. Together, they represent one of the most chemically diverse libraries in nature.

In his landmark 2014 book Plants and the Human Brain, neuroscientist David O. Kennedy of Northumbria University makes an argument that deserves far wider attention: plant secondary metabolites have not merely coexisted with human neurobiology; they have actively shaped it. Over millions of years of co-evolution, human brain chemistry adapted to expect, process, and respond to these compounds. We did not simply tolerate the chemistry of the plant world around us; we incorporated it into our biology.

The mechanism through which plants interact with other organisms is called allelopathy: the chemical influence that one organism exerts on another through the release of secondary metabolites into the environment. These relationships take three forms, each with its own logic:

Synomones are allelochemicals that benefit both the plant that produces them and the organism that receives them. A plant that releases compounds attracting a pollinator is producing a synomone; the plant gets pollinated, the insect gets nectar. Many of the plant-human interactions involving terpenes appear to fall into this category.

Kairomones benefit the receiver at the expense of the producer. Some trees release terpenes that attract bark beetles, which then attract the beetles' predators; a chemical chain reaction in which the tree ultimately loses.

Allomones benefit the producer at the receiver's expense; deterrent compounds, toxins, and repellents that protect the plant without necessarily harming the recipient.

What makes human-plant allelopathy remarkable is the sheer depth of the co-evolutionary record. Humans and their hominid ancestors have been embedded in plant-rich environments for millions of years. Our genomes bear the evidence: we have developed specific metabolic pathways for processing plant secondary metabolites, specific receptors that bind to them, and specific physiological responses that they trigger. The chemistry of plants is not foreign to our bodies. In many respects, it is expected by them.

Part Two: Terpenes

The Most Abundant, Most Diverse, and Most Biologically Active Secondary Metabolites

Of the three classes of plant secondary metabolites, terpenes are the largest, the most chemically diverse, and, I would argue, the most significant for human health. There are more than 35,000 named terpenes. They are found in every plant on earth. They are, more than anything else, responsible for the smells of the natural world: the sharp resinous scent of a pine forest, the sweetness of orange peel, the floral complexity of jasmine, the warm spice of black pepper.

Terpenes are classified by the number of isoprene units in their molecular structure:

Monoterpenes (two isoprene units): the most common, highly volatile, immediately aromatic. Limonene, alpha-pinene, linalool.
Sesquiterpenes (three isoprene units): less volatile, deeper and more complex aromas. Beta-caryophyllene, farnesene.
Diterpenes (four isoprene units): less volatile still, found in resins. Taxol, cafestol.
Triterpenes (six isoprene units): largely non-volatile, present in plant waxes and sterols. Squalene.
Tetraterpenes (eight isoprene units): carotenoids, including beta-carotene. Responsible for the orange of carrots and the red of tomatoes.

For the purposes of this discussion, the monoterpenes and sesquiterpenes are most relevant, because they are the ones we actually breathe. Their volatility is what carries them into the air and into our lungs and olfactory systems.

What Terpenes Do in the Human Body

Terpenes are not passive. When inhaled, they enter the body through two primary pathways: the olfactory epithelium, where they bind directly to olfactory receptors and trigger neurological signals, and the respiratory mucosa, where they are absorbed into the bloodstream. From either pathway, they reach the brain and the broader systemic circulation, where they interact with a remarkable range of biological targets.

The most studied of these interactions involve the endocannabinoid system, the endocrine system, and the neuroendocrine system: the three primary regulatory systems through which the body maintains homeostasis.

Consider a few of the most well-documented terpene-receptor interactions:

Limonene, the terpene responsible for the smell of citrus, is one of the most abundant monoterpenes on earth. Research has linked its inhalation to reductions in stress biomarkers, including cortisol levels and sympathetic nervous system activity. A 2014 study by d'Alessio and colleagues demonstrated anti-stress effects of d-limonene and its metabolite perillyl alcohol in animal models. Limonene appears to interact with serotonin and dopamine receptors, suggesting a mechanism for its mood-associated effects.

Alpha-pinene, the dominant terpene in coniferous trees and one of the most abundant terpenes in the global atmosphere, has been studied for its effects on alertness and memory. It is a known acetylcholinesterase inhibitor (meaning it may preserve the neurotransmitter acetylcholine, which plays a centra)l role in attention and learning. You can read more about alpha-pinene's terpene profile here.

Myrcene, found abundantly in hops, lemongrass, and mangoes, is the most common terpene in cannabis and interacts with opioid receptors to produce sedative effects. It is also believed to facilitate the transport of other terpenes across the blood-brain barrier, functioning as a kind of biochemical escort. More on myrcene here.

Linalool, the primary terpene in lavender, has the most extensive clinical literature of any aromatic terpene. Dozens of studies document its effects on stress, sleep quality, and mood: effects mediated through GABA-A receptor modulation, the same receptor system targeted by many pharmaceutical sedatives.

Beta-caryophyllene is unusual among terpenes in that it directly binds to CB2 receptors in the endocannabinoid system (making it technically a dietary cannabinoid, despite being found in black pepper), cloves, and many common herbs. Its anti-inflammatory and analgesic properties are well documented in preclinical research.

The picture that emerges from this research is not of a few pleasant-smelling molecules with minor effects. It is of a large class of biologically active compounds that interact with the body's most fundamental regulatory systems in measurable, reproducible ways. These are not novelties. They are inputs that our biology evolved to receive.

Terpenes and the Global Ecosystem

The biological significance of terpenes extends beyond human health. These compounds are planetary in their importance. Terpene aerosols released above forests seed clouds: forests can, through their terpene emissions, actually influence their own rainfall patterns (Huff Hartz et al., 2005). Terpenes regulate the growth of neighboring plants, influence soil microbiology, attract or repel specific insects, and mediate complex multi-species relationships that have taken millions of years to develop.

When you walk into a dense forest and breathe deeply, you are not simply enjoying a pleasant smell. You are inhaling a living chemical ecosystem: a molecular record of millions of years of co-evolutionary chemistry, most of which science has only begun to characterize.

Part Three: The Long Relationship

Human-Plant Co-Evolution and What It Means for Our Biology

The story of human evolution is inseparable from the story of plants. This is obvious at the dietary level: we are what we eat, and for most of human history, what we ate was plants, or animals that had eaten plants. But the relationship goes deeper than nutrition.

For millions of years, hominids and then Homo sapiens lived in environments saturated with plant secondary metabolites. Every breath taken by every human ancestor, back through geological time, included terpenes. Our bodies did not evolve in a botanical vacuum: they evolved in a botanical symphony.

The evidence for this deep integration is written into our genomes. A classic example involves amylase, the enzyme responsible for starch digestion. About 10,000 years ago, as humans began cooking and consuming tubers in significant quantities, selection pressure favored individuals with more copies of the amylase gene. The average human genome today contains six copies of the AMY1 gene, compared to one or two copies in genomes from before cooking (Perry et al., 2007). Our diet changed; our genome followed. This is co-evolution: the biological record of a sustained relationship with a class of foods.

The same logic applies to terpenes. If our ancestors breathed terpene-rich air for millions of years, it is not unreasonable to expect that our biology would have developed receptors, metabolic pathways, and physiological responses calibrated to that input. The evidence that it has is not written in single gene variants but in the extraordinary specificity with which human receptor systems respond to plant secondary metabolites: the fit between botanical compound and human receptor that is too precise to be coincidental.

Archaeogenomic research supports this view. Allaby and colleagues (2015) documented what they describe as "plant-hominin co-evolution" pushing back as far as the Pliocene; establishing that the relationship between human ancestors and the plant world is not a recent development but a foundational feature of what it means to be human.

Forest Therapy: The Research

The most direct contemporary evidence for the biological importance of plant terpenes to human health comes from the Japanese practice of Shinrin-yoku, or forest bathing: the practice of spending extended time in forest environments with the deliberate intention of taking in the forest atmosphere through all the senses.

What began as a public health initiative in Japan in the 1980s has since generated a substantial body of peer-reviewed research. The findings are consistent and striking. In studies by Song, Ikei, and Miyazaki (2016), subjects who spent time in forest environments showed significant reductions in cortisol, lower blood pressure, reduced sympathetic nervous system activity (measured by heart rate variability), and improved mood compared to urban controls performing the same physical activities. The forest was doing something that the urban environment was not: and crucially, studies that controlled for physical activity confirmed that the benefits were not simply the result of walking.

Perhaps the most dramatic findings involve immune function. Immunologist Qing Li of the Nippon Medical School in Tokyo conducted studies in which participants who spent two days in a forest showed significant increases in natural killer (NK) cell activity: cells that play a central role in immune surveillance and the destruction of virus-infected and tumor cells. The elevated NK cell activity persisted for more than 30 days after the forest exposure (Li, 2010). Li subsequently identified specific terpene compounds: particularly alpha-pinene and other phytoncides released by Japanese cypress trees: as likely mechanisms for this immune activation.

Studies by Ikei, Song, and Miyazaki (2015) further demonstrated that olfactory stimulation with Hinoki cypress leaf oil: containing terpene concentrations similar to those found in forest air; produced measurable physiological effects including reductions in sympathetic nervous system activity, even without the full forest environment. The terpenes themselves, delivered through inhalation, were producing the effect.

This is important. It means the mechanism is chemical, not merely psychological. People do not simply feel better in forests because forests are peaceful. They feel better, in part, because specific molecular compounds are interacting with specific biological systems in specific, measurable ways.

You can explore the science of forest bathing in more depth here.

Part Four: Paleo Air

What Our Ancestors Breathed, and Why It Matters

The concept of the Paleo Diet rests on a straightforward premise: our digestive systems evolved over millions of years in response to specific foods; lean meats, vegetables, fruits, nuts, seeds; and the chronic diseases of modern civilization may be partly explained by the mismatch between that evolutionary diet and the ultra-processed, high-sugar, high-refined-carbohydrate diet that most people in wealthy countries now consume.

I find this evolutionary mismatch framework compelling: not as a complete explanation of modern disease, but as a useful lens for examining the gap between what our biology expects and what it actually gets. And when I apply that lens to the air we breathe rather than the food we eat, what I see is a mismatch of potentially equal significance.

I call the ancestral atmospheric environment Paleo Air.

Paleo Air is the terpene-rich, botanically complex air that humans and their ancestors breathed for hundreds of thousands of years: in forests, on grasslands, along coastlines, in the diverse outdoor environments where our species evolved. It is air that contained the volatile secondary metabolites of hundreds of plant species simultaneously: the monoterpenes of conifers, the sesquiterpenes of flowering plants, the phytoncides of ancient trees, the mineral-rich marine aerosols of the ocean.

There is no single chemical formula for Paleo Air. Its composition varied by region, season, and ecosystem. But its defining characteristic was botanical richness: a complex, layered mixture of thousands of terpene and non-terpene volatile compounds, constantly varying, never reduced to a single source.

What We Breathe Instead

The US Environmental Protection Agency estimates that Americans spend approximately 90 percent of their time indoors. Indoor air, by essentially any measure, is not Paleo Air.

EPA research consistently shows that indoor air pollutant levels are often two to five times higher than outdoor levels: and in some cases, significantly more. The sources of these pollutants include building materials, furniture, cleaning products, synthetic fragrances, combustion byproducts, and biological contaminants including mold and dust mite debris. An extreme manifestation of this phenomenon is what occupational health researchers call "Sick Building Syndrome": a documented pattern of acute health complaints including headaches, fatigue, cognitive impairment, and respiratory irritation that appear to be directly linked to the quality of indoor air.

But indoor air is not simply more polluted than forest air. It is also radically depleted. The monoterpenes and sesquiterpenes that characterize Paleo Air are almost entirely absent from typical indoor environments. The botanical volatiles that our biology evolved to process are simply not there.

The result is something I would describe as a kind of atmospheric monoculture: air that is biologically inert from the perspective of the terpene-responsive systems in the human body. We have not merely added pollutants to the air. We have subtracted a complex, biologically active chemistry that our bodies expect to receive.

It is worth noting that outdoor urban air is not Paleo Air either. Even time spent outdoors in most cities provides only a fraction of the botanical terpene exposure that characterizes genuine forest or meadow environments. A walk through a concrete urban center, however pleasant, does not replicate the atmospheric chemistry of the forest our ancestors inhabited.

For a deeper exploration of Paleo Air and its relationship to modern aromatherapy, see the original Paleo Air overview and Paleo Air and the benefits of modern aromatherapy.

Part Five: Terpene Deficiency

A Framework for Understanding What Modern Air Is Missing

If Paleo Air is what we evolved to breathe, and modern air is largely depleted of the botanical compounds that characterized Paleo Air, then the logical question is: what are the consequences of that depletion for human health?

I have proposed a working framework for thinking about this question, which I call Terpene Deficiency: or, in its more formal articulation, Terpene Deficiency Syndrome (TDS).

Let me be precise about what this is and what it is not.

Terpene Deficiency is not a recognized medical diagnosis. It does not appear in the DSM or the ICD. There is no blood test for it, no clinical criteria, no pharmaceutical treatment. I am not proposing it as a disease entity. I am proposing it as a theoretical framework: a conceptual tool for organizing a set of observations that otherwise lack a coherent explanation.

The framework rests on a straightforward analogy: Terpene Deficiency is to plant secondary metabolites what Vitamin D deficiency is to sunlight.

Vitamin D deficiency was not always understood. For much of history, the cluster of symptoms associated with severe Vitamin D deficiency: rickets, bone pain, immune dysfunction, depression; these were treated as separate, unrelated problems. The insight that unified them was the recognition that the human body requires sunlight-mediated Vitamin D synthesis to function correctly, and that modern indoor living systematically deprives many people of adequate sunlight exposure. Once that framework was established, the pattern of symptoms became intelligible as a coherent syndrome.

I am proposing a parallel framework for terpenes. The human body has evolved to receive a complex input of botanical volatile compounds through inhalation. Modern indoor living systematically reduces that input toward near-zero. What are the consequences?

What Terpene Deficiency May Look Like

The honest answer is that we do not yet know, because the formal hypothesis has not been tested in clinical trials. What we do have is a constellation of observations that the framework helps to organize:

Seasonal Affective Disorder (SAD) is perhaps the most suggestive parallel. SAD arrives with winter and resolves in spring: the same seasonal pattern as the dormancy of terpene-producing plants. Every year, as the trees lose their leaves and flowering plants go dormant, the terpene content of outdoor air drops significantly. The same season reliably produces elevated rates of mood disruption, fatigue, changes in appetite, and immune challenges in a substantial portion of the population.

For decades, SAD was attributed entirely to reduced sunlight exposure and its effects on serotonin and melatonin. Reduced sunlight is almost certainly part of the story. But it may not be the whole story. The simultaneous reduction in atmospheric terpenes: compounds that have documented interactions with serotonin receptor systems, as demonstrated in limonene research: deserves consideration as a contributing factor that has not yet been adequately investigated.

Urban-rural health disparities are another suggestive pattern. Epidemiological research consistently documents better mental health outcomes in rural and suburban environments compared to dense urban ones, even after controlling for socioeconomic factors. The reasons are complex and multifactorial, but the dramatically higher terpene exposure available to people living near forests, parks, and diverse green spaces is a plausible contributing factor.

The general malaise of modern sedentary indoor life: the chronic low-grade fatigue, mood instability, reduced cognitive resilience, and impaired sleep that many people experience: is not fully explained by any single factor. Poor diet, sedentary behavior, blue light exposure, social isolation, and chronic stress all contribute. But the near-complete depletion of botanical terpenes from the air most people breathe for most of their lives may be an underappreciated contributor.

What the Terpene Deficiency framework offers is not a claim that terpene depletion explains all of this: it clearly does not. But a claim that it may explain some of it, and that the hypothesis deserves serious scientific investigation.

For a more detailed discussion of how terpenes interact with the body's homeostatic systems, including the endocannabinoid, endocrine, and neuroendocrine systems, see Keeping Your Body Systems in Check with Terpenes. For a concise FAQ on Terpene Deficiency Syndrome, see Understanding Terpene Deficiency. The broader terpenes and terpene deficiency hub provides additional resources.

Part Six: The Research Landscape

What We Know, What We Don't, and What Needs Study

The scientific foundation for the Terpene Deficiency and Paleo Air frameworks varies considerably by domain. Some areas are well-established. Others are promising but underexplored. And the specific hypothesis of Terpene Deficiency as a coherent syndrome remains, for now, in the realm of the proposed rather than the confirmed.

What Is Well-Established

Forest therapy effects are real and reproducible. The body of peer-reviewed research on Shinrin-yoku, while concentrated in Japan, is methodologically solid and consistent in its findings. Measurable reductions in cortisol, blood pressure, and sympathetic nervous system activity following forest exposure have been replicated across multiple research groups and populations.

Specific terpenes produce specific physiological effects. The research on limonene, alpha-pinene, linalool, and beta-caryophyllene is not anecdotal. These compounds have been tested in controlled settings, their receptor interactions have been characterized, and their physiological effects have been measured. The mechanisms are not mysterious: they are specific, biochemical, and in many cases well-understood.

NK cell activity increases with forest exposure and with terpene inhalation. Li's research on this point is among the most striking in the field. The magnitude of the immune response: and its persistence for over a month following a two-day forest exposure; this suggests that something clinically significant is happening, not merely a transient physiological fluctuation.

Indoor air quality is a documented public health problem. The EPA, WHO, and a substantial body of occupational health research document the negative health consequences of poor indoor air quality. Sick Building Syndrome is a recognized clinical entity. The contribution of terpene depletion: as distinct from pollutant addition (rather than pollutant addition) in indoor air health effects is less studied, but the broader point is established: the air quality of the environments where most people spend most of their time is genuinely problematic.

What Remains to Be Studied

Terpene Deficiency Syndrome as a formal hypothesis has not been tested in clinical trials. The specific question: whether chronic terpene depletion produces a measurable, reproducible pattern of wellness challenges that can be attenuated by terpene supplementation: has not been the subject of a controlled study. This is an open area, and an important one.

The dose-response relationship for inhaled terpenes is not well characterized. Forest air contains terpenes at concentrations of roughly 1-20 micrograms per cubic meter for the dominant species, with total terpene loads in the range of several hundred micrograms per cubic meter in dense forest. Indoor air typically contains far less. What the therapeutic threshold might be: the minimum terpene exposure needed to produce measurable physiological benefits remains unknown.

The synergistic effects of terpene mixtures deserve much more investigation than they have received. Most terpene research tests single compounds in isolation. But the biological context in which these compounds evolved; and in which our biology evolved to process them; it is one of extraordinary mixture and complexity. Forest air does not contain one terpene; it contains hundreds simultaneously. The interactions between them, including what researchers in cannabis science call the "entourage effect," may be essential to the biological response. Single-terpene research may systematically underestimate the importance of these compounds by removing them from the complex mixture context in which they are most effective.

Part Seven: Restoring Paleo Air

Practical Approaches to Bridging the Terpene Gap

If the arguments above are correct: that our biology evolved to receive a complex, botanically rich atmospheric input that modern life has largely eliminated: then the practical question is what to do about it. The answer involves a spectrum of approaches, from the most natural to the most technologically mediated.

Genuine Forest Time

The most direct way to breathe Paleo Air is to go where Paleo Air still exists. That means genuine forest environments: not manicured urban parks, not suburban green spaces, but forests with the botanical diversity and density that produce significant terpene loads in the air. Coastal forests, old-growth stands, and ecologically diverse woodlands are the highest-value environments for this purpose.

The Shinrin-yoku research suggests that two hours of intentional forest immersion is a meaningful dose: enough to produce measurable physiological effects. The protocol is simple: walk slowly, put the phone away, breathe deeply, and engage all the senses. The goal is not exercise but exposure: atmospheric, sensory, botanical.

Even shorter, more frequent exposures are likely beneficial. Regular time in terpene-rich outdoor environments: several times per week; this seems more protective than a single extended annual visit to a forest, in the same way that regular exercise confers more benefit than a single intense exertion.

Diverse Plant Life in Indoor and Transitional Spaces

Indoor plants produce terpenes at lower concentrations than outdoor forest environments, but they are not negligible. A substantial collection of botanically diverse plants: herbs, flowering plants, conifers where space permits: these can introduce some measure of terpene chemistry into indoor air. This is partial mitigation, not a solution, but partial mitigation is worth having.

Gardens, green rooftops, and transitional spaces that allow genuine plant-air interaction contribute meaningfully to the atmospheric terpene environment of those who use them regularly.

Essential Oils and Botanical Aromatherapy

Essential oils are concentrated terpene preparations: the volatile secondary metabolites of plants, extracted and preserved. When diffused appropriately, they introduce terpenes into indoor air at concentrations that may be biologically meaningful.

A critical point here, which is easy to miss: a single essential oil is not Paleo Air. A bottle of lavender essential oil delivers a handful of terpene species, predominantly linalool and linalyl acetate. A bottle of sweet orange delivers limonene with trace compounds. These are not trivial: both compounds have documented biological effects. But forest air delivers hundreds of terpene species simultaneously, and the synergistic interactions between them are likely as important as the individual components.

This is the argument for blended aromatherapy: for using combinations of essential oils from many different botanical sources rather than single-origin oils. The broader the botanical base of a blend, the closer it approaches the terpene complexity of the natural environment. A well-designed blend of twelve or fifteen essential oils from ecologically diverse plant families introduces a far richer terpene palette than any single oil, and begins to approach: though it does not replicate the chemical complexity of the forest air it is meant to invoke.

Portable personal aromatherapy devices using carefully formulated botanical blends represent one practical tool within this broader framework. They are not a substitute for genuine forest time, but they make terpene exposure accessible in the contexts: commuting, working at a desk, traveling (contexts where forest time is not available).

Explore MONQ's full collection of botanical aromatherapy diffusers if you want to explore this approach in practice.

Part Eight: The Larger Frame

Why This Matters Beyond Wellness

The concept of evolutionary mismatch: the idea that many features of modern life create a gap between what our biology was designed for and what it actually experiences: has become one of the more productive frameworks in contemporary medicine and public health.

The Paleo Diet movement popularized the dietary version of this argument: our digestive systems evolved for ancestral foods, and the processed diets of modern industrial civilization are a form of biological mismatch with predictable health consequences. Researchers studying barefoot running argue that shoes represent a form of mismatch between foot anatomy and terrain. Sleep researchers have documented the mismatch between our circadian biology and the artificial lighting environments of modern life. The common thread is the recognition that evolution is slow and culture is fast: and the gap between what our biology was built for and what it actually experiences is a legitimate source of disease burden.

Terpene Deficiency and Paleo Air fit squarely within this framework. They are not fringe ideas. They are the atmospheric dimension of an argument that is already well-established in multiple other domains of human biology.

The science of forest therapy is peer-reviewed and published in major journals. The receptor interactions of specific terpenes are documented in the pharmacological literature. The concept of the entourage effect: the biological synergy between terpene mixtures that exceeds the effects of individual compounds: is increasingly established in plant science, following its development in cannabis research. The idea that plants and humans have co-evolved in ways that make plant secondary metabolites biologically important to human health is not a fringe proposition. It is increasingly mainstream.

David Kennedy's Plants and the Human Brain (2014) remains the most comprehensive single account of this co-evolutionary relationship. Kennedy's argument: that the human brain did not develop its remarkable capabilities in isolation, but in intimate chemical conversation with the plant world: provides the theoretical foundation for everything I have described above. The brain our species has is, in part, a brain that evolved in Paleo Air. Removing that atmospheric input without understanding the consequences seems, at minimum, worth taking seriously.

A Note on Intellectual Provenance

The terms Terpene Deficiency, Terpene Deficiency Syndrome, and Paleo Air, as applied to human health, were coined by me, Eric Fishman, M.D.: in the course of founding and developing MONQ beginning in 2014. Prior uses of "terpene deficiency" in the scientific literature refer exclusively to terpene content in plants, not to human health conditions. No prior use of these terms in the human health context has been documented.

I make this note not for reasons of vanity, but because the intellectual genealogy of ideas matters when those ideas begin to circulate more widely. If these concepts prove useful: if they give researchers, clinicians, or wellness practitioners a framework for thinking about atmospheric terpene exposure and human health; I want the origin to be clearly documented.

Conclusion: Look Up

I want to end with an image.

Imagine standing at the edge of an old-growth forest: the kind of place where the canopy is thick enough that the light filters through in shafts, where the ground is layered with decades of leaf litter, where the air has a density to it that you can almost feel. You take a breath and something happens. Your shoulders drop. Your mind quiets. Your heart rate, if you measured it, would be lower than it was five minutes ago in the parking lot.

Most people attribute this to aesthetics. The forest is pretty. It's relaxing. The absence of city noise is a relief. These things are true. But they are not the whole story.

What is also happening, invisibly, is a cascade of molecular interactions that evolution has been refining for millions of years. The monoterpenes from the conifers are binding to olfactory receptors and triggering neurological responses. The phytoncides are activating immune pathways. The complexity of the atmospheric chemistry: hundreds of compounds simultaneously, at concentrations our biology evolved to process: is doing something to you that no amount of "relaxing music" or "nature sounds" audio track replicates. The chemistry is real. The biology responding to it is real. The effect is measurable.

What I am suggesting is that this is not merely a pleasant experience. It is a biological necessity: or something approaching one. That the air most of us breathe, for most of our lives, is impoverished in exactly the compounds our biology was built to expect. And that the consequences of this impoverishment: diffuse, non-specific, easy to attribute to a dozen other causes; these symptoms may be adding up in ways we have not yet adequately reckoned with.

I am not claiming certainty. I am proposing a hypothesis and inviting serious inquiry. Terpene Deficiency and Paleo Air are frameworks, not diagnoses. The research that would confirm or modify them has not yet been done at the scale or rigor it deserves.

But the direction of the existing evidence: the forest therapy literature, the terpene pharmacology, the co-evolutionary record, the Kennedy synthesis: all points the same way. The air matters. The chemistry of the air matters. And we have been largely ignoring it.

So: go to the forest when you can. Breathe deliberately when you are there. Take the terpene question seriously. And pay attention to how you feel in different air.

The answers may be in the next breath you take.

References

Kennedy, D.O. (2014). Plants and the Human Brain. Oxford University Press.
Li, Q. (2010). Effect of forest bathing trips on human immune function. Environmental Health and Preventive Medicine, 15, 9-17.
Song, C., Ikei, H., & Miyazaki, Y. (2016). Physiological effects of nature therapy: a review of the research in Japan. International Journal of Environmental Research and Public Health, 13(8), 781.
Perry, G.H. et al. (2007). Diet and the evolution of human amylase gene copy number variation. Nature Genetics, 39, 1256-1260.
d'Alessio, P.A. et al. (2014). Anti-Stress Effects of d-Limonene and Its Metabolite Perillyl Alcohol. Rejuvenation Research, 17(2), 145-149.
Ikei, H., Song, C., & Miyazaki, Y. (2015). Physiological effect of olfactory stimulation by Hinoki cypress (Chamaecyparis obtusa) leaf oil. Journal of Physiological Anthropology, 34, 44.
Huff Hartz, K.E. et al. (2005). Cloud condensation nuclei activation of monoterpene and sesquiterpene secondary organic aerosol. Journal of Geophysical Research: Atmospheres, 110(D14).
Allaby, R.G. et al. (2015). Archaeogenomic insights into the adaptation of plants to the human environment. Journal of Human Evolution, 79, 150-157.
US Environmental Protection Agency. (2022). Indoor Air Quality. EPA.gov. Retrieved from https://www.epa.gov/report-environment/indoor-air-quality

About the Author: Eric Fishman, M.D., is a physician, entrepreneur, and the founder of MONQ, the personal aromatherapy company he started in 2014. He coined the concepts of Terpene Deficiency, Terpene Deficiency Syndrome, and Paleo Air as frameworks for understanding the relationship between atmospheric terpene exposure and human wellness. MONQ is based in Goodlettsville, Tennessee.

Disclaimer: The above information is provided for general wellness and educational purposes only. Please note that while individual essential oil ingredients may have been shown to exhibit certain independent effects when used alone, the specific blends of ingredients contained in MONQ diffusers have not been tested. No specific claims are being made that use of any MONQ diffusers will lead to any of the effects discussed above. Additionally, please note that MONQ diffusers have not been reviewed or approved by the U.S. Food and Drug Administration. MONQ diffusers are not intended to be used in the diagnosis, cure, mitigation, prevention, or treatment of any disease or medical condition. If you have a health condition or concern, please consult a physician or your alternative health care provider prior to using MONQ diffusers. MONQ blends should not be inhaled into the lungs. Why? It works better that way. No Nicotine Ever in MONQ Pens. Inhale through the mouth, exhale through the nose. MONQ Diffusers are not intended for individuals under 18, or women who are pregnant or nursing.

Terpene Deficiency & Paleo Air: The Science Behind What Modern Life Takes From Us