by Jade Shutes, B.A., Dipl. AT, Cert. Herbalist
Based upon our Aromatic Chemistry program, this manual is a printed version of research on both essential oils and components that will support your work in clinical aromatherapy practice, home care self care, or simply to provide you with valuable research to refer to in order to support therapeutic efficacy of various aromatic products.
In our “Components and Essential Oils – A Research Reference Manual” we cover not only current research on a wide range of essential oils but also how different components found within essential oils contribute to this activity. The reference manual includes quick reference therapeutic charts based upon the material presented as well as an extensive reference section. Deepen your understanding of monoterpenes, sesquiterpenes, monoterponols, sesquiterpenols, aldehydes, ketones, phenols, and more!
Here is a small example of what you will learn throughout our “Components and Essential Oils – A Research Reference Manual”.
General Composition of Monoterpene Hydrocarbon Rich Essential Oils
|α-pinene(4.4-31%), β-pinene (0.2-1.48%), p-cymene (3.5-11.3%), myrcene (1.4-5.5%), cis-ocimene syn. β-ocimene (1.-1.9%), β-phellandrene (10-30%), delta-3-carene (4.5-13%), sabinene (0.4-1.2%), and α-phellandrene (2-20%), Camphene (0.2-1.43%)1|
|α-pinene (4.2-12.8%), sabinene (2.5-4.6%), myrcene (2-2.5%), delta-3-carene (t-0.5%), β-phellandrene (33.6 – 65%)2&3|
|limonene (10.54-34.88%), α-terpinene (0-0.23%), α-pinene (0-0.79%), α-thujene (0.15-0.29%), myrcene (0.26-0.77%), terpinolene (0.28-0.57%)4|
|limonene (31.66%), α-terpinene (0.30%), α-pinene (0.88%), α-thujene (0.29%), myrcene (1.33%), terpinolene (0.57%)5|
|Black pepperPiper nigrum||d-limonene (15.22-35.06%), α-pinene (7.35-16.68%), (-)-car-3-ene (5.51-32%) and β-pinene (10.2-13%), α-phellandrene (0.75-2.88%)6&7|
Limonene, a naturally occurring hydrocarbon, is a cyclic monoterpene with the molecular formula C10H16. It is commonly found in the rinds of citrus fruits such as grapefruit, lemon, lime and, in particular, oranges. Limonene has two enantiomers: (+)-limonene (d-limonene) and (-)-limonene (l-limonene).
Enantiomers have identical chemical and physical properties except for their ability to rotate plane-polarized light (+/-) by equal amounts but in opposite directions. Enantiomers interact differently with other chiral molecules i.e. biologically active molecules as amino acids, sugars, steroids, etc. This means that some molecules have, for example (enantiomiers of limonene), different odors.9
The two enantiomers have identical chemical properties but different odours. (+)-Limonene (d-limonene) is the isomer that is found in oranges. And unsurprisingly it smells of oranges! The smell of (-)-limonene is similar to turpentine, although some people suggest it has a lemon like aroma.
Now lets have a look at research on limonene and essential oils rich in limonene:
- Limonene, α-pinene, and germacrene – High antioxidant activity The main compounds of oils showing high antioxidant activity were limonene (composition, 74.6%) in celery seed, benzyl acetate (22.9%) in jasmine, alpha-pinene (33.7%) in juniper berry, myristicin (44%) in parsley seed, patchouli alcohol (28.8%) in patchouli, citronellol (34.2%) in rose, and germacrene (19.1%) in ylang-ylang.[i]
- d-limonene has been clinically used to dissolve cholesterol-containing gallstones. It has also been used for relief of heartburn/GERD, because of its gastric acid neutralizing effect and improvement of peristalsis. D-limonene has well-established chemopreventive activity against many types of cancers. Evidence from a phase I clinical trial shows a partial response in a patient with breast cancer and stable disease for more than six months in three patients with colorectal cancer.[ii]
- limonene exhibits anxiolytic activity. At concentrations of 0.5% and 1.0%, (+)-limonene, administered to mice by inhalation, significantly modified all the parameters evaluated in the elevated plus maze test. The pharmacological effect of inhaled (+)-limonene (1%) was not blocked by flumazenil. These data suggest possible connections between the volatility of (+)-limonene and its anxiolytic-like effect on the parameters evaluated in the elevated plus maze test. The data indicate that (+)-limonene could be used in aromatherapy as an antianxiety agent.[xii]
- Litsea cubeba and d-limonene exhibit anxiolytic and analgesic activity. In addition, both the essential oil and one of its constituent monoterpenes, d-limonene, were found to possess potent anxiolytic and analgesic activities based on the results obtained from elevated plus-maze and writhing tests.[xiii]
- Another study on the anxiolytic activity of limonene. These findings suggest that acute administration of the (+)-limonene epoxide exerts an anxiolytic-like effect on mice, and it could serve as a new approach for the treatment anxiety, since it practically does not produce toxic effects.[xiv]
- limonene exhibits fungicidal activity against Trichophyton rubrum. (Trichophyton rubrum is known to be the most common causative agent of dermatophytic nail infections in humans.) Our results demonstrated that the volatile vapor of limonene at concentrations greater than 1 μl/800 ml air space profoundly inhibited the growth of T. rubrum. After the removal of essential oil from the Phytatrays, no resumption of cell growth was noted after 72 h of incubation, thereby indicating the fungicidal activity of the volatile limonene. Direct application of limonene in the broth microdilution assay also revealed limonene’s potent fungicidal effects against T. rubrum. Therefore, our results indicated that the treatment of fungal cells with limonene might result in an alteration in the integrity of the cell membrane.[xv]
- Oxidized limonene is a skin sensitizer. Pure limonene is a weak contact allergen in experimental studies and seldom causes positive patch test reactions in dermatitis patients in clinical studies. Autoxidation of limonene, the primary oxidation products, the hydroperoxides (limonene-1-hydroperoxide and limonene-2-hydroperoxide), are the most potent allergens in the oxidation mixture.[xvi]
Research on essential oils rich in limonene
- Citrus oils exhibit anxiolytic and sedative action. In general, we can conclude that EOs from Citrus latifolia (Persian lime), Citrus reticulata (Mandarin) and Citrus aurantium (Bitter orange) peels presents anxiolytic and sedative activity in rodents, without motor impairment. Positive results in anxiety experimental procedures are related to both generalized anxiety and obsessive-compulsive disorders. Observed results are probably due to a synergistic action of the common compounds present in the three species.[xvii] Essential oils obtained from ripe fruit peels of C. latifolia and C. reticulata elicited anxiolytic and sedative effects. The limonene was the main compound in these essential oils, 58 and 90%, respectively.[xviii]
- Citrus sinensis (Sweet orange) oil demonstrated anxiolytic activity. These results suggest an acute anxiolytic activity of sweet orange essence, giving some scientific support to its use as a tranquilizer by aromatherapists.[xix]
- Citrus limon has sedative, anxiolytic and antidepressant activities.[xx]
- Citrus limon has antioxidant activity. Our findings strongly support the hypothesis that oxidative stress in hippocampus can occur during neurodegenerative diseases, proving that hippocampal damage induced by the oxidative process plays a crucial role in brain disorders, and also imply that a strong protective effect could be achieved using EO of Citrus limon (L.) Burms (Rutaceae) as an antioxidant.[xxi]
- Our results support that the essential oil of Citrus limon exhibits an antioxidant action in preventing lipoperoxidation (probably due to hydroxyl radical scavenging activity) and a clear antinociceptive activity. [xxii]
- Fennel (Foeniculum vulgare) demonstrates anti-inflammatory activity. We can say that the anti-inflammatory effect of Fennel essential oil is thought to be due to limonene, α-pinene and β-pinene. However, all other constituents of fennel essential oil may contribute to that activity.[xxiii]
- Bergamot (Citrus bergamia) has anxiolytic activity.[xxiv]
- Lemon (Citrus limon) is effective penetration enhancer for vitamins held in w/o or o/w emulsions. Lemon EO produced only reversible modification of Transepidermal Water Loss (TEWL), and it is a safe and effective penetration enhancer for topical administration of lipid- and water-soluble vitamins.[xxv]
- Lemon essential oil is antidepressant and anxiolytic. These findings suggest that the antidepressant-like effect of lemon oil is closely related with the 5-HTnergic pathway, especially via 5-HT(1A) receptor. Moreover, the lemon oil significantly accelerated the metabolic turnover of DA in the hippocampus and of 5-HT in the prefrontal cortex and striatum. These results suggest that lemon oil possesses anxiolytic, antidepressant-like effects via the suppression of DA activity related to enhanced 5-HTnergic neurons.[xxvi]