Aromatic Chemistry NEW! Online Program

The School for Aromatic Studies is incredibly pleased to announce the launch of our new
Advanced Aromatic Chemistry

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Course Overview

lavandula stoechas

To learn more about the technical aspects of this program, please visit here.

Insights into the new program:

Aromatic Chemistry will teach you not only about the current research on a wide range of essential oils but also how components of different essential oils contribute to this activity. Here is a small example of how the material is presented in the course. Note: this listing is much more extensive in course.

General Composition of Monoterpene Hydrocarbon Rich Essential Oils

Essential Oil

Monoterpenes Content

Angelica root Angelica archangelica 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
Angelica seedAngelica archangelica 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
BergamotCitrus bergamiaCOLD PRESSED 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
Bergamot Citrus bergamiaDISTILLED 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

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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).

Recall from Module 1: 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]
  • d-limonene possesses immunomodulatory activity.[iii]&[iv]
  • d-limonene exhibits antioxidant activity.[v]&[vi]
  • limonene exhibits sedative and motor relaxant activity.[x]&[xi]
  • 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 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]


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[i]  Wei A. & Shibamoto T. (2007). Antioxidant activities and volatile constituents of various essential oils. J Agric Food Chem. 2007 Mar 7;55(5):1737-42. Epub 2007 Feb 13. Retrieved from PMID: 17295511 on March 12, 2007 from

[ii]  Sun J. (2007). D-Limonene: Safety and Clinical Applications. Alternative Medicine Review Volume 12, Number 3.

[iii]  Del Toro-Arreola S, Flores-Torales E, Torres-Lozano C, Del Toro-Arreola A, Tostado-Pelayo K, Guadalupe Ramirez-Duenas M, and Daneri-Navarro A. Effect of d-limonene on immune response in BALB/c mice with lymphoma. International Immunopharmacology, Vol5, Issue 5, May 2005, Pages 829–838

[iv] Lappas C M and Lappas N T.  d-Limonene modulates T lymphocyte activity and viability. Cellular Immunology, Vol. 279, Issue 1, September 2012, Pages 30–41.

[v] Malhotra S, Suri S, Tuli R. Antioxidant Activity of Citrus Cultivars and Chemical Composition of Citrus karna Essential Oil. Planta Med 2009; 75(1): 62-64

[vi] Santiago J V A, Jayachitra J, Shenbagam M, Nalini N. d-limonene attenuates blood pressure and improves the lipid and antioxidant status in high fat diet and L-NAME treated rats. J. Pharm. Sci. & Res. Vol.2 (11), 2010,752-758

[vii]  Miller J A, Thompson P A, Hakim I A, Lopez A M, Thomson C A, Chew W, Hsu CH, and  Chow HH S. Safety and Feasibility of Topical Application of Limonene as a Massage Oil to the Breast Journal of Cancer Therapy, 2012, 3, 749-754.

[viii] Haag J D, Lindstrom M J, and Gould M N. Limonene-induced regression of mammary carcinomas.  Cancer Res 1992;52:4021-4026. Retrieved on January 28, 2013 from:

[ix] Anitha P, Jaikumar S, Kamaraj S, Devaki T. Antioxidant and anticancer efficacy of D-Limonene in Benzo(A)pyrene lung carcinogenesis in mice. Drug discovery, 2012, 1(1), 9-16

[x] do Vale TG, Furtado EC, Santos JG Jr., Viana GS. Central effects of citral, myrcene and limonene, constituents of essential oil chemotypes from Lippia alba (Mill.) n.e. Brown. Phytomedicine. 2002 Dec;9(8):709-14.

[xi] do Vale T G, Furtado E C, Santos Jr. J G, and Viana G S B. Central effects of citral, myrcene and limonene, constituents of essential oil chemotypes from Lippia alba (Mill.) N.E. Brown. Phytomedicine, Vol 9, Issue 8, 2002, Pages 709–714

[xii] Lima NG, De Sousa DP, Pimenta FC, Alves MF, De Souza FS, Macedo RO, Cardoso RB, de Morais LC, Melo Diniz Mde F, de Almeida RN. Anxiolytic-like activity and GC-MS analysis of (R)-(+)-limonene fragrance, a natural compound found in foods and plants. Pharmacol Biochem Behav. 2013 Jan;103(3):450-4.

[xiii] Chen C-J, Tseng Y-H, Chu F-H, Wen T-Y, Cheng W-W, Chen Y-T, Tsao N-W, Wang S-Y. Neuropharmacological activities of fruit essential oil from Litsea cubeba Persoon. J Wood Sci (2012) 58:538–543

[xiv] de Almeida AA, Costa JP, de Carvalho RB, de Sousa DP, de Freitas RM. Evaluation of acute toxicity of a natural compound (+)-limonene epoxide and its anxiolytic-like action. Brain Res. 2012 Apr 11;1448:56-62.

[xv] Chee H Y, Kim H, Lee M H. In vitro Antifungal Activity of Limonene against Trichophyton rubrum. Mycobiology 37(3) : 243-246 (2009)

[xvi] Christensson, JB. (2009). Thesis paper: Clinical and Experimental Studies on Oxidized Fragrance Terpenes as Contact Allergens. Department of Dermatology and Venereology, Sahlgrenska University Hospital, Institute of Clinical Sciences at Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden

[xvii] Costa Gargano A, Almeida Costa C A R, Costa M. Essential Oils from Citrus latifolia and Citrus reticulata Reduce Anxiety and Prolong Ether Sleeping Time in Mice. Tree and Forestry Science and Biotechnology 2 (Special Issue 1), 121-124.

[xviii] Pimenta, Fernandes F C, de Azevedo C N, Gondin Dias K L, De Sousa, Peregrino D, Da Rosa, Diniz M R, Pimenta, Fernandes M B, de Fatima Formiga Melo M, De Almeida, Nobrega R. Naturally occurring anxiolytic substances from aromatic plants of genus citrus. Journal of Medicinal Plants Research Vol. 6(3), pp. 342-347, 23 January, 2012

[xix] Faturi CB, Leite JR, Alves PB, Canton AC, Teixeira-Silva F. Anxiolytic-like effect of sweet orange aroma in Wistar rats. Prog Neuropsychopharmacol Biol Psychiatry, 2010 May 30;34(4):605-9.

[xx] L M Lopes C, Goncalves e S C, de Almeida AA, da Costa JP, Marques TH, Feitosa CM, Saldanha GB, de Freitas RM. Sedative, anxiolytic and antidepressant activities of Citrus limon (Burn) essential oil in mice. Pharmazie. 2011 Aug;66(8):623-7.

[xxi] Campelo LM, Goncalves FC, Feitosa CM, de Freitas RM. Antioxidant activity of Citrus limon essential oil in mouse hippocampus.  Pharm Biol. 2011 Jul;49(7):709-15.

[xxii] Campelo LML, de Almeida A A C, Mendes de Freitas R L, Cerqueira G S, de Sousa G F, Saldanha G B, Feitosa C M, Mendes de Freitas R.  Antioxidant and Antinociceptive Effects of Citrus limon Essential Oil in Mice. Journal of Biomedicine and Biotechnology, Volume 2011 (2011), Article ID 678673, 8 pages

[xxiii] Ozbeck, H. The Anti-Inflammatory Activity of Foeniculum vulgare L. Essential Oil and Investigation of its Median Lethal Dose in Rats and Mice. International Journal of Pharmacology, 1(4): 329-331, 2005.

[xxiv] Saiyudthong S, Marsden CA. Acute effects of bergamot oil on anxiety-related behaviour and corticosterone level in rats. Phytother. Res. 2011 Jun;25(6):858-62. doi: 10.1002/ptr.3325. Epub 2010 Nov 23.

[xxv] Valgimigli L, Gabbanini S, Berlini E, Lucchi E, Beltramini C, Bertarelli YL. Lemon (Citrus limon, Burm.f.) essential oil enhances the trans-epidermal release of lipid- (A, E) and water- (B6, C) soluble vitamins from topical emulsions in reconstructed human epidermis. International Journal of Cosmetic Science, Vol 34 (4), pages 347–356, August 2012

[xxvi] Komiya M, Takeuchi T, Harada E.  Lemon oil vapor causes an anti-stress effect via modulating the 5-HT and DA activities in mice. Behav Brain Res. 2006 Sep 25;172(2):240-9