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A plant's growing conditions (e.g., climate, raw material use, and region), harvesting, distillation (essential oils extraction from the plant), manufacturing, and sourcing all can impact the constituents present, their qualities, and the predominant chemotype (metabolites within a certain species) of an essential oil.48,49
A 2012 article in Alternative Medicine stated the following regarding how distillation duration and temperature changed chemical composition of a specific species of frankincense:
Chemical constituents of Boswellia sacra essential oil fractions were dependent on duration and temperature of hydrodistillation. For example, when essential oils collected from 0–2 h (Fraction I), 8–10 h (Fraction II), and 11–12 h (Fraction III) at 78 °C were compared, longer distillation produced higher percentages of sesquiterpenes, between alpha-copaene and caryophyllene oxide (Table 1). All three fractions were primarily composed of monoterpenes (82.77–90.67%), including alpha-thujene, beta-pinene, and myrcene. Among the monoterpenes, alpha-pinene was the major compound present in all essential oil fractions, ranging from 65.49% to 78.45%. As anticipated, the abundance of alpha-pinene decreased with longer and higher temperature distillation due to its highly volatile nature. Compounds such as borneol, dimethyl ether or-cinol, allo-aromadendrene, gamma-cadinene, and caryophyllene oxide were only present in Fraction III essential oil…
We found that boswellic acids contents depended on hydrodistillation duration and temperature (Table 2). Essential oils prepared from longer distillation time and higher distillation temperature contained greater amounts of boswellic acids. For example, boswellic acids contents in Fractions III (19.6%) and IV (30.1%) were higher than those detected in Fraction I (0.9%) or II (0.8%) essential oil.52
In a review article on lavender essential oil and its impact on the nervous system, the authors stated their concern with the validity of the research of essential oils' efficacy due to these quality issues, including methodological and oil identification problems:
The dried lavender flowers used in some trials were sourced from a local herb store (i.e., ). Although taxonomic identification was confirmed in these studies, without quantification of key constituents the quality of the herbal product may be questionable . Although some studies defined the contents of lavender, it is essential that all future clinical studies specify the exact derivation of the oils used in the study and, preferably, include a profile of the liquid or the percentage composition of the major constituents. In addition, several factors, such as temperature, skin type and quality, and the size of area being treated, which may affect the level and rate of lavender absorption after massage or aromatherapy, were not considered in several investigations. Many discreet compounds in lavender oil have shown a myriad of potential therapeutic effects, and researchers continue to seek novel treatments to different ailments .53
Therefore, it's important to determine the quality of the essential oil when using them for therapeutic applications, such as pain modulation. Furthermore, processed or synthetic compounds added to essential oils could have unintended effects on physiology.
Emotions and Essential Oils: To the Macroscopic Viewpoint
The use of essential oils for their aromatic influence, mood-enhancing benefits, as well as their biochemical and physiological modulation, makes them a holistic and therapeutic intervention for pain. For example, depression is a complex syndrome and is often associated with chronic pain.54-59
The complexity of factors relating to depressive symptoms is too intensive to review in this article; however, one small study examined several factors related to its symptomatology through studying various parameters following the inhalation of the essential oil clary sage (Salvia sclarea). The study consisted of 22 menopausal women in their 50s. Researchers measured changes in 5-hydroxytrypatmine (5-HT), cortisol, and thyroid stimulating hormone (TSH), as well as differences from baseline in the Korean version of Beck Depression Inventory-I (KBDI-I), KBDI-II, and Korean version of Self-rating Depression Scale after exposure to the essential oil.60
Clary sage essential oil was selected for this trial due to its reported antidepressant actions on dopamine pathways in animal studies and its suggested estrogen effects, which impact neurotransmitter levels.60,61 The study demonstrated that clary sage oil showed an "indirect depression reduction effect in terms of reduced plasma cortisol and TSH concentration and increased plasma 5-HT concentration." The authors noted that only the KBDI-II showed significant differences in association with 5-HT and cortisol levels in normal and depressive subjects, indicating that this subjective measurement may be a more accurate reflection of the biochemical changes in depression.
The authors concluded, "When using KBDI-I and KBDI-II, 5-HT increased by 341% and 828% for the normal group and 484% and 257% for the depression tendency group, respectively. The change rate of cortisol was greater in depression tendency groups compared with normal groups, and this difference was statistically significant when using KBDI-II (31% vs. 16% reduction) and Self-rating Depression Scale inventory (36% vs. 8.3% reduction). Among three inventories, only KBDI-II differentiated normal and depression tendency groups with significantly different cortisol level."
Limitations to this study include generalizability to males, small sample size, and heterogeneity.60 Yet, this study demonstrated that an essential oil can modulate hormonal and neurological support through physiological effects of the constituents present and the psychological responses known to occur from the odor itself.
More extensive support for the use of essential oils on various emotions and regulation of physiology in clinical, in vitro, and in vivo trials was presented in a 2006 article, "Aromatherapy in the Management of Psychiatric Disorders: Clinical and Neuropharmacological Perspectives." The term pyschoaromatherapy was used in order to more precisely label the impact of essential oils in the more pronounced psychiatric disorders. This is due to the fact that the researchers perceived the term aromatherapy to be an incomplete portrayal of essential oils' effects. They understood that responses to the oils aren't necessarily related to the aroma of the volatile compounds alone.
Therefore, in this review, the dual nature of the "indirect" and "direct" effect of aroma was examined. Specifically, the authors sought to determine how the emotional aspect of the odor (direct effect) along with the effects of the biochemical constituents (indirect effect) affected psychological disorders, mood, and physiological response patterns. The article explained:
The effects of an aroma can be instantaneous and include both direct and indirect psychological effects – even thinking about a smell may have a similar effect to the smell itself. However, accumulating evidence that inhaled or dermally applied essential oils enter the blood stream and, in relevant molecular, cellular or animal models, exert measurable psychological effects, indicates that the effects are primarily pharmacological. This conclusion is supported by increasingly reported benefits of aromatherapy using specific essential oils in the management of chronic pain, depression, anxiety and some cognitive disorders, as well as insomnia and stress-related disorders.
Within this review was a comprehensive overview of the many aspects of assessing the efficacy and mechanisms of essential oils in psychology in several ways. First, the authors presented a thorough report on the pharmacological actions and central nervous effects of the main constituents found in various essential oils, as determined by in vitro and in vivo studies. Second, chemical constituents of aromatic essential oils relevant to cerebral function were evaluated. Third, clinical trials relating to mood disorders, including comprehensive trials using essential oils for dementia, were also described. (Noteworthy were several intriguing clinical trials with Alzheimer's patients who demonstrated behavioral improvement with the use of essential oils, e.g., lemon balm and lavender.) Finally, the importance of the difference responses of the ANS (autonomic nervous system) to essential oils (i.e.; stimulating versus calming effects) were highlighted. These final results supported anecdotal reports familiar essential oils such as lavender being relaxing and rosemary being more stimulating. The authors' overall conclusions were:
It is concluded that aromatherapy provides a potentially effective treatment for a range of psychiatric disorders. In addition, taking into account the available information on safety, aromatherapy appears to be without the adverse effects of many conventional psychotropic drugs. Investment in further clinical and scientific research is clearly warranted.62
Due to the fact that odors can be cued stimuli producing fear and anxiety and resultant pain response, mitigating these negative aromatic effects with calming and psychologically balancing essential oils could beneficial in treating chronic pain patients.30-40 According to a summary from a 1999 article in Alternative Therapies in Health and Medicine:
Chronic pain consumes approximately $70 billion per year and affects some 80 million Americans. Increasingly, aromatherapy has been used as part of an integrated, multidisciplinary approach to pain management. This therapy is thought to enhance the parasympathetic response through the effects of touch and smell, encouraging relaxation at a deep level. Relaxation has been shown to alter perceptions of pain. Even if one ignores the possibility that essential oils have pharmacologically active ingredients – or the potential pharmacokinetic potentization of conventional drugs by essential oils – aromatherapy might possibly play a role in the management of chronic pain through relaxation.63
In one review of 16 randomized controlled clinical trials relating to the use of essential oils and anxiety, the authors stated:
Most of the studies indicated positive effects to quell anxiety. No adverse events were reported.64
The effects of essential oils on emotion alone could constituent a series of lengthy articles. For the purpose of this article, I will now focus on some specific studies relating to the mechanism of pain modulation with essential oils as well as clinical trials. You will discover that we have come a long in explaining the relevance of "psychoaromatherapy."
Zeroing Back in On the Microscopic Mechanisms of Essential Oils for Antinociception
A 2016 review article analyzed 31 essential oils for their antinociceptive activity in animal models of nociception. The authors assessed the botanical aspects of these aromatic plants, their mechanisms of action, and the chemical composition profiles of the essential oils. The most common chemical constituent categories of monoterpenes, sesquiterpenes, and phenylpropanoids were the focus for the authors. To enhance understanding of mechanisms involved, descriptions of the pain models used in the studies to determine analgesia were included.
Specifically, these tests, and their percentage of frequencies in the studies reviewed, included: acetic acid-induced writhing (72.2%), formalin (66.7%), hot plate (27.8%), tail flick (11.1%), and tail immersion (5.6%). Inflammatory pain was evaluated in 22.2% of the studies, as associated with the carrageenan test. Peripheral or central mechanisms involved in pain processing were determined by the pathway induced by the specific test used. Furthermore, many studies validated particular modes of action through comparison of well-known agonist and antagonist pain medications.65
For instance, the formalin model of nociception was used to discriminate pain into its central and peripheral components. This is accomplished through its two different test phases that are separated in time. In the first phase, direct formalin action is generated in the periphery through activation of nociceptive neurons. The second phase activates the ventral horn neurons at the spinal cord level.65,66 The narcotic drug morphine inhibits nociception in both phases, indicating dual action, whereas indomethacin and corticosteroids inhibit only the second phase, indicating a peripheral action. Drugs blocking prostaglandin synthesis, such as acetylsalicylic acid and paracetamol, also block only the second phase of the formalin test. Authors in the trials reviewed also concluded that mild analgesics (such as aspirin) can initiate antinociceptive activity in tonic tests (writhing and formalin tests), but lack analgesic results in thermal tests, such as the hot-plate test.66
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