What it is:
Humans have utilized plant medicines for centuries, and many indigenous peoples still harness this ancestral wisdom. In modern society, we have forgotten about many of these natural healing compounds, relying instead on synthetic, pharmacologic interventions to cure us of our ails. But there’s something to be said about looking to nature as a first-line treatment, given all that it provides for us.
Aromatherapy is the ancient practice of using plant-derived essential oils for a therapeutic benefit. This form of natural medicine has been used for centuries to remedy poor mood and stress, as well as promote a healthy immune system. There is documented use in civilized societies worldwide, such as incense in China, Roman baths, and embalming rituals in Egypt.
The term “aromatherapy” was coined by a French chemist named Rene-Maurice Gattefosse in the late 1920s. After a lab explosion badly burned his head and hands and gangrene began to rear its ugly head, Gattefosse recalled a conversation with a lavender grower who had once told him of the plant’s potent healing properties. Gattefosse proceeded to coat his burns with lavender oil and - somewhat miraculously - two days later noticed that his wounds had healed. The news spread fast throughout the scientific community, catalyzing the use of concentrated plant oils in the Western world throughout the twentieth century — a practice that has only increased in popularity.
As well as offering antimicrobial benefits, essential oils are often championed for their mood-altering effects. Some scents are uplifting, giving us the get-up and go, while others are associated with relaxation, even having potential benefits on sleep. Much of the evidence out there is anecdotal, though an increasing body of literature now documents how some of these compounds have been put to the test in a more rigorous scientific setting.
While it might be a while before Western doctors begin prescribing essential oils for health, a review of the science suggests they may be a beneficial addition to existing wellness routines. Unless the oils are being ingested or applied directly to the skin without a carrier oil to dilute them, they are unlikely to be harmful, and that’s particularly appealing to those seeking more natural ways of promoting relaxation and sleep.
The purported claims:
Essential oils contain a variety of different volatile compounds that may alleviate anxiety and/or depression.
Some of these compounds have been shown to modulate various neurotransmitter systems throughout the brain.
Aromatherapy can modulate sleep architecture and quality and may act through both psychologic and physiologic mechanisms.
What the science says:
In 1982, the Forest Agency of Japan began promoting forest bathing trips as a way for people to manage their stress levels and improve their quality of life. Shinrinyoku is now practiced by many people in Japan as well as other forested countries around the world. It involves, quite simply, spending time amongst the trees either while sedentary or gently walking.
Scientists have shown that forest bathing boosts mental health and immunity. The verdant surroundings, fresh air, and volatile plant compounds likely contribute to healthy outcomes. In a study where participants spent a few hours either walking around a city or a forest, urine levels of adrenaline (also called epinephrine) were significantly lower in the forest walkers up to seven days after their trip.
There is now good evidence to show that aromatherapy can potently modulate our autonomic nervous system. In a study that involved applying a carrier oil either with or without linalool (a significant component of lavender essential oil) to participants’ abdominal areas, the linalool addition resulted in a subsequent decrease in blood pressure. Essential oils are typically detected in the bloodstream 10-20 minutes after application on the skin. Linalool is known to dilate blood vessels, hence the blood pressure-lowering effects seen in this study.
Many people interact with essential oils via scented sprays and diffusers. In this form, the oils do not have contact with the skin but are inhaled. Inhalation allows these plant-derived compounds to enter the body either through the olfactory bulb or - probably to a lesser degree - through the lungs.
Our sense of smell is interesting as it is a direct conversation between odor molecules and the brain. “Smelling” occurs when an odor molecule enters the nose and binds to an olfactory sensory neuron, which sends the signal to other areas of the brain for interpretation. This might include the prefrontal cortex, responsible for executive function and decision-making, or the limbic system, which governs processes below the conscious thinking level, such as those of emotional memories and the fear response.
Japanese researchers have shown that lavender essential oil can modulate GABA activity, an important neurotransmitter system involved in sedation and sleep. It was shown that when lavender oil was present in the brains of their animal model (an aquatic frog), less GABA was needed in order to produce the same sleep-promoting effects. In this experiment, lavender was considered a “potentiator” of GABA activity. This means that while it couldn’t replace the role of healthy GABA release in creating a sleepy response, it was able to make the frogs require less of it. In other words, it supported sedation.
Other research has shown that alongside dopamine and serotonin neurons, essential oils can also work on the GABA system. St. John’s Wort, while typically consumed rather than inhaled, is used by many for its anti-depressive properties. This plant extract has been shown to act like a natural selective serotonin reuptake inhibitor (SSRI), preventing the reuptake of serotonin (along with dopamine) back up into neurons. This promotes the positive mood state that we associate with higher levels of these neurotransmitters. It is likely that some essential oil-derived compounds are able to act similarly via the olfactory system.
Lavender also inhibits glutamate binding (a neurotransmitter associated with wakefulness) and reduces intracellular cyclic adenosine monophosphate (cAMP) levels. cAMP is an important chemical messenger that facilitates many different processes within many cells. The combination of these two mechanisms may be one of the ways that lavender promotes the sedation that many people associate with it.
A recent meta-analysis of multiple studies that investigated the effects of aromatherapy on sleep in older adults found that there were benefits to sleep quality, stress, pain, and mood symptoms such as anxiety and depression after aromatherapy use. Another meta-analysis of ten different randomized controlled trials (considered the most rigorous way of testing a compound) found that aromatherapy helped cancer patients’ sleep.
Few aromatherapy studies have been conducted with the rigor that we typically see in drug trials. Without that data, it’s hard to draw robust conclusions. However, several studies have produced interesting findings that warrant attention. In one experiment, participants were exposed to peppermint oil before having their sleep measured objectively using polysomnography. Interestingly, those who rated the peppermint scent as being more stimulating showed more non-rapid eye movement (NREM) sleep that night. Those who rated the peppermint as more sedating took longer to enter deep, slow-wave sleep that night. The investigators also noted some potential sex differences, whereby the peppermint oil appeared to be more stimulating for men and more sedating for women. Peppermint oil is generally associated with many positive benefits, including digestive support and even better athletic performance. Still, this discrepancy between subjective feelings about the scent and objective sleep architecture should be further probed.
The problem with studies where participants are asked to smell an essential oil before reporting their mood is that they cannot be “blinded” to the experimental condition. We can have many associations with specific smells (what we might consider classic “Pavlovian conditioning”). So regardless of the physiological mechanisms at play when two people inhale the same essential oil, if one has had a negative past experience associated with that smell, the beneficial effects may be blunted compared to the person who associates the scent with a positive mood.
Pleasant smells can evoke pro-social behavior. In a study where people were exposed to the scent of baked goods and brewed coffee in a mall, they were likelier to help a stranger. This might be because we associate these odors with home and safety; thus, we may be more altruistic when these sensory experiences are evoked.
The best evidence to suggest that essential oils can improve sleep comes from a study in which the researchers released the odor into the air after the participants had fallen asleep. Lavandula augustifolia was released in pulses every 5 minutes across the night from 1.5 hours after sleep onset, until approximately 1.5 hours before waking. During a control condition, participants were exposed to pulses of water vapor only.
During the lavender condition, participants’ slow wave (deep) sleep increased, and participants reported better sleep quality and daytime performance the next day. These were healthy sleepers with no self-reported sleep problems, but it raises the question of whether we can optimize sleep, even among those without disorders. The American College of Physicians still recommends cognitive behavioral therapy for insomnia (CBTi) as the first-line treatment for insomnia disorder. However, the scientific community is eager to continue investigating ways that people without disordered sleep can still maximize its benefits. Aromatherapy may be a risk-free way of optimizing health without resorting to medications.
Our take:
When delving into aromatherapy, it's essential to consider what you are trying to achieve. There is a wide range of claims surrounding the practice, and it's crucial to remember that the FDA does not regulate nor classify "essential oils". There are many possible ways of utilizing aromatherapy, so follow the scientific research and make decisions based on your needs.
For example, incorporating aromatherapy into a wind-down routine can benefit those grappling with mild stress-induced sleep disturbances. Utilizing essential oils in conjunction with activities like massage or a warm bath enhances relaxation and may contribute to overall improved sleep quality.
The selection of oils is a highly personal choice, intertwined with how scents evoke emotional memories. An intriguing example is wintergreen, perceived as pleasant in the United States (associated with candy) and unpleasant in the United Kingdom (linked to the scent of medicine and analgesics). Or Linalool, a key compound in essential oils found in over 200 plants, suggests that even if lavender isn't preferred, alternatives might evoke similar mildly sedating effects or other potential benefits.
Still curious to try it? If you do, here’s what to look out for:
Many studies that have evaluated the effects of essential oil compounds in rodents have done so via intraperitoneal injection. Given that this is not how humans interact with aromatherapy products, if you do your own research, be sure to look out for studies in which the animals or human participants are treated via topical application or olfaction.
If you decide to try an essential oil, seek out the highest quality products you can. Look for companies with a demonstrated history of quality control checks and purity testing. Ensure the product label displays the Latin name of the plant, an ingredients list, and the country of origin. You should seek out organic essential oils with lower levels of concentrated pesticides and source products that are environmentally and worker-friendly.
To prevent photo-degradation, essential oils and fragrances should be stored in dark bottles (amber or blue-tinted glass). Lastly, avoid blends that contain fillers (“i.e., ‘parfum”), which are typically synthetic and may be associated with hormone disruption.
References and additional materials:
Gattefosse “father of aromatherapy” - https://www.fondation-gattefosse.org/en/rene-maurice-gattefosse/
Forest bathing and immunity - https://pubmed.ncbi.nlm.nih.gov/19568839/
Forest bathing vs city-bathing on immunity - https://pubmed.ncbi.nlm.nih.gov/18336737/
Meta-analysis of older adults - https://pubmed.ncbi.nlm.nih.gov/34166869/
Meta-analysis of sleep in cancer patients - https://pubmed.ncbi.nlm.nih.gov/35836211/
Essential oils and GABA activity - https://academic.oup.com/bbb/article/63/4/743/5946458
Lemon oil and brain activity - https://pubmed.ncbi.nlm.nih.gov/16780969/
An overview of aromatherapy mechanisms - https://pubmed.ncbi.nlm.nih.gov/19125379/
St. John’s Wort and 5-HT - https://pubmed.ncbi.nlm.nih.gov/10543427/
Prosocial behavior and odors - https://pubmed.ncbi.nlm.nih.gov/22822681/
Odors and athletic performance - https://www.sciencedirect.com/science/article/abs/pii/S0031938423003335
Sleep and peppermint oil study - https://pubmed.ncbi.nlm.nih.gov/16143443/
Sleep and lavender oil study - https://pubmed.ncbi.nlm.nih.gov/33441798/
Aromatherapy and mood disorders - https://pubmed.ncbi.nlm.nih.gov/35496310/
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