AromaChemistry and Applications of Tea Tree Oil – Part 1 of 4

Introduction

Plants, as a means of chemical defense, produce and store a variety of compounds that help protect against invasion from microorganisms. As a result, many of these compounds possess a multitude of medicinal qualities for humans. An extract of Melaleuca alternifolia, commonly known as Tea Tree, has been used within the practice of Medicinal Aromatherapy for a vast array of conditions. This plant is indigenous to Australia and has been used by the Aborigines for thousands of years as a form of natural medicine. The extract is acquired via steam distillation from the leaves of Melaleuca alternifolia, and the resulting product is coined an essential oil (1).

Essential Oils are the extracts of volatile compounds to which plants attribute their scent and fragrance.   Essential Oil extracts are isolated and obtained via steam distillation or other methods from various plant parts, including the leaves, stems, fruits, and/or roots. Far exceeding the role of a mere aroma, these mixtures are commonly associated with antimicrobial, antifungal, antiseptic, and antibacterial properties, or some combination thereof. Tea Tree Oil (TTO) has been noted for many of these effects, although rigorous research is still ongoing. TTO is currently incorporated into pharmaceutical and holistic products for both its preservative and therapeutic qualities. Of its most acknowledged uses, Tea Tree Oil is applied topically to treat acne, dandruff, onychomycosis (toe nail fungus), cuts, and cold sores, although scientific studies to fully support these treatments and determine Tea Tree Oil’s mode of action are pending (1).

Chemistry

Many constituents of Tea Tree Oil are compounds that belong to the chemical family, Terpenes. This family comprises mainly hydrocarbons, although some molecules are oxygen-containing and include alcohols, ketones, and aldehydes. The building blocks of terpene molecules are units of isoprene, which have the molecular formula C₅H₈. Thus, terpene molecules without derivation or alteration will have a formula of (C₅H₈)_n, where n represents the number of repeating isoprene units. The structure of isoprene is as follows: CH₂=C(CH₃)-CH=CH₂. Coincidentally, many of the molecules found in tea tree are isomers. Three common isomers found in Tea Tree Oil have the formulas C₁₀H₁₆, C₁₀H₁₈O, and C₁₅H₂₄ (2). The major components, their classification, and chemical formula are defined in Table 1 (1).

Table 1

Classification of TTO Components

Due to the inherent variability of the natural world, in conjunction with the fact that TTO has approximately 100 components, two TTO compositions are rarely the same. To set criteria for standardization, the International Organisation of Standardisation (IOS) has established a range of composition for the major components of TTO (Table 2).

Table 2.

^a IOS 4730, International Organization for Standardization standard no. 4730 (from reference 3)
^b From reference 4
^c No upper limit is set, although 48% has been proposed.
^d No lower limit is set.

Chemotypes

There are six known chemotypes of Melaleuca alternifolia, all comprising very unique chemical compositions. The chemotypes are classified by the distinct percentage presence of a specific component. The chemotypes include a terpinen-4-ol chemotype, a terpinolene chemotype, and four 1,8-cineole chemotypes. The terpinen-4-ol chemotype is the one that is repeatedly used in commercial production, and typically contains 30-40% terpinen-4-ol (1). It is notable that the 1,8-cineole chemotypes have not been utilized in commercial production, due to erroneous accounts of its action as a skin and mucous membrane irritant (4).  Due to this fact, few studies have been conducted reviewing 1,8-cineole and consequently, little is actually known about the molecule itself and its function in TTO.

References

1. Carson, C.F., K.A. Hammer, and T.V. Riley. “Melaleuca alternifolia (Tea Tree) Oil: A Review of Antimicrobial and Other Medicinal Properties.” Clinical Microbiology Reviews (2006): 50-62.
2. Kirste, B. 2 February 2002. 7 October 2008 <http://www.chemie.fu-berlin.de/chemistry/oc/terpene/terpene_en.html>.
3. International Organisation for Standardisation. 2004. ISO 4730:2004. Oil of Melaleuca, terpinen-4-ol type (tea tree oil). International Organisation for Standardisation, Geneva, Switzerland.
4. Brophy, J.J., N.W. Davies, I.A. Southwell, I.A. Stiff, and L.R. Williams. “Gas Chromatographic Quality Control for Oil of Melaleuca Terpinen-4-ol Type (Australian Tea Tree).” Journal of Agricultural and Food Chemistry (1989): 1330-1335.
5. Carson, C.F. and T.V. Riley. “Antimicrobial activity of the major components of the essential oil of Melaleuca alternifolia.” Journal of Applied Bacteriology (1995): 264-269.
6. Carson, C.F., B.J. Mee, and T.V. Riley. “Mechanism of Action of Melaleuca alternifolia (Tea Tree) Oil on Staphylococcus aureus Determined by Time-Kill, Lysis, Leakage, and Salt Tolerance Assays and Electron Microscopy.” Antimicrobial Agents and Chemotherapy (2002): 1914-1920.
7. Cox, S.D., J.E. Gustafson, C.M. Mann, J.L. Markham, Y.C. Liew, R.P. Hartland, H.C. Bell, J.R. Warmington, and S.G. Wyllie. “Tea tree oil causes K+ leakage and inhibits respiration in Escherichia coli.” Letters in Applied Microbiology (1998): 355-358.
8. Gustafson, J.E., Y.C. Liew, S. Chew, J. Markham, H.C. Bell, S.G. Wyllie, and J.R. Warmington. “Effects of tea tree oil on Escherichia coli.” Letters in Applied Microbiology (1998): 194-198.
9. Mann, C.M., S.D. Cox, and J.L. Markham. “The outer membrane of Pseudomonas aeruginosa NCTC 6749 contributes to its tolerance to the essential oil of Melaleuca alternifolia (tea tree oil).” Letters in Applied Microbiology (2000): 294-297.
10. Bassett I.B., D.L. Pannowitz, and R.S. Barnetson. “A comparative study of tea-tree oil versus benzoylperoxide in the treatment of acne.” Medical Journal of Austrailia (1990): 455-458.
11. Satchell, A.C., A. Saurajen, C. Bell, and R. Barnetson. “Treatment of dandruff with 5% tea tree oil shampoo.” American Academy of Dermatology (2002): 852-855.
12. Golab, M., and K. Skwarlo-Sonta. “Mechanisms involved in the anti-inflammatory action of inhaled tea tree oil in mice.” Experimental Biology and Medicine (2007): 420-426.
13. Koh, K.J., A.J. Pearce, G. Marshman, J.J. Finlay-Jones, and P.H. Hart. “Tea tree oil reduces histamine-induced skin inflammation.” British Journal of Dermatology (2002): 1212-1217.
14. Halcon, L., and K. Milkus. “Staphylococcus aureus and wounds: A review of tea tree oil as a promising antimicrobial.” American Journal of Infection Control (2004): 402-408.
15. Cross, S.E., M. Russell, I. Southwell,and M.S. Roberts. “Human skin penetration of the major components of Australian tea tree oil applied in its pure form and as a 20% solution in vitro.” European Journal of Pharmaceutics and Biopharmaceutics 69 (2008): 214-222.
16. Hammer, K.A., C.F. Carson, T.V. Riley, and J.B. Nielsen. “A review of the toxicity of Melaleuca alternifolia (tea tree) oil.” Food and Chemical Toxicology (2006): 616-625.

Continue Reading: AromaChemistry and Applications of Tea Tree Oil – Part 2 →