Melaleuca alternifolia, commonly known as the narrow-leaved paperbark and narrow-leaved tea-tree, is tall flowering shrub or tree of the Myrtaceae family that is native to Australia.

The long, narrow leaves of this plant possess prominent oil glands from which Melaleuca, or tea tree, oils are extracted. Aborigines of Australia were the first to use the leaves as medicine, crushing them and applying them to skin infections and bug bites. Other uses involved chewing, or boiling of the leaves and inhalation of the steam to relieve head aches or respiratory ailments. It wasn’t until the 1920s that research was done regarding tea tree oil’s medicinal effects. A study into the oil’s antiseptic effects revealed that it was 11 times more potent than the medical gold standard antiseptic currently in use (Carson, et al. 2006).

Melaleuca alternifolia tree. Photo by Tangopaso (Own work) [Public domain], via Wikimedia Commons

Melaleuca alternifolia leaves. Photo by Raffi Kojian (http://Gardenology.org) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Although “tea tree oil” can be extracted from many different plants, today it is primarily derived from the leaves and terminal branches of M. alternifolia through a steam distillation process. Tea tree oil is an increasingly popular essential oil used in alternative medicine. The oil is most widely recognized for its antimicrobial effects, although it does possess numerous other properties including antibacterial, antifungal, anti-inflammatory, antiviral, analgesic properties, and more. Today, the plant is cultivated on a commercial scale and used in a variety of health care products. The company Melaleuca is well known for introducing the healthful benefits of the melaleuca oil into the world marketplace, producing over 400 different products ranging from personal health, nutritional, and home care products, essential oils, and more. Their goal is to integrate more alternatives to the harsh chemicals used in many of the cleaning and care products found in the market today.

Studies have found that over 100 terpenes and their associated alcohols have been identified in the oil thus far. Gas Chromatography analysis by the International Organization for Standardization (ISO) lists 15 terpenes as the major components of the oil (ISO 4730:2004).

The antimicrobial effects of tea tree oil originate partially from terpinen-4-ol, a terpene compound that is usually the highest in content out of the 15 specified by the ISO. Since 1996 there has been a regulated international standard for the composition of terpinen-4-ol type tea tree oil. This regulation requires that the terpinen-4-ol content must be above 30% and the 1,8-cineole content muss be less than 15%. These unbalanced proportions stem from the early views of 1,8-cineole being a mucus membrane and skin irritant and terpinen-4-ol as the primary beneficial agent. Recent studies have disproven this fact, although it is still standard for terpinen-4-ol levels to be at least twice that of 1,8-cineole. There has been an increasing need for new antimicrobial agents as the development of resistance to existing agents has become more common.

terpinen-4-ol

While many antimicrobial, and antiseptic compounds in general, usually target processes involving the production or synthesis of new cells, terpinen-4-ol  targets the cytoplasmic membrane of a cell (Carson, et al. 2002). Oregano, rosewood, and thyme are three other examples of extremely antimicrobial oils commonly used in alternative medicine. Carvacol, citronellol, geraniol, and thymol, which are the most active antimicrobial agents of these oils are not found in M. alternifolia oil. The antibacterial components of Melaleuca oil affect the lag and exponential growth phases of bacteria, suggesting that their target is not a molecular synthetic process, but rather the stationary phase of growth in the organism. Once compromised, the cytoplasmic membrane of the cell leaks nucleic acid and other essentials, causing a slow decrease in cell functions and integrity until the cell is destroyed by its own enzymes.

A study into the mechanisms of action of terpinen-4-ol against Staphylococcus aureus showed that while terpinen-4-ol is a major player in the antibacterial effects of tea tree oil, other compounds such as 1,8-cineole and α-terpineol work together to create a complex defensive system with a diverse set of mechanisms. S. aureus and many gram-negative bacteria have been found to be more susceptible to the bactericidal effects of tea tree oil in contrast to gram-positive bacteria. Upon exposure, gram-positive bacteria are unable to reproduce but not necessarily killed by the oil. These results suggest that tea tree oil may have a unique ability to remove harmful transient bacteria from the skin while only suppressing the reproduction of harmless resident skin flora (Hammer, et al. 1996). Given that tea tree oil is made up of over 100 different terpenes, it is unlikely that there is only one chemical or mechanism of action that is responsible for the antimicrobial effects exhibited by the oil (Carson, et al. 2002). Further investigation into the heterogenous composition of tea tree oil is required to fully understand its effects and the processes involved.

There is still much more research to be done on tea tree oil and its potential therapeutic and medicinal effects. Many of the inconclusive or unsuccessful studies that have been done are in part due to the oil’s hydrophobic nature, making it hard to measure and study using traditional liquid analysis methods. Other sources of confusion stem from the loose differentiation between the oils distilled from Melaleuca and Eucalyptus genera, both of which contain high levels of 1,8-cineole and belong to the Myrtaceae family. While being very similar, the difference in their chemical composition has led to varied results in studies done in its safety and properties. There are a number of other chemically distinct oils distilled from other Melaleuca species such as cajuput oil and niaouli oil. While similar, the difference in their chemical makeup has produced varied results from studies into the properties of “melaleuca oil”. As this oil has become more popular in natural and alternative medicine, it has become increasingly accessible. Clinical studies have shown promising results in the ability to harness the use tea tree oil’s potent properties. Further analysis of the safety and efficacy of this oil could lead to an increased integration of its use in the medical and scientific world. 

Sources cited:

Carson CF, Thomas RV. 2001. Safety, efficacy and provenance of tea tree (Melaleuca alternifolia) oil. Contact Dermatitis [Internet]. [cited 2017 Jan. 14]; 45(2): 65-67. http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0536.2001.045002065.x/abstract

Carson CF, Mee BJ, Riley TV. 2002. 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 [Internet]. [cited 2017 Feb. 9]; 46(6): 1914-1920. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC127210/

Hammer KA, Carson CF, Thomas RV. 1996. Susceptibility of transient and commensal skin flora to the essential oil of Melaleuca alternifolia (tea tree oil). American Journal of Infection Control [Internet]. [cited 2017 Feb. 5]; 24(3): 186-189. http://www.sciencedirect.com.evergreen.idm.oclc.org/science/article/pii/S0196655396900115

Hammer KA, Carson CF, Thomas RV. 2006. Melaleuca alternifolia (Tea Tree) Oil: a Review of Antimicrobial and Other Medicinal Properties. Clinical Microbiology Reviews [Internet]. [cited 2017 Jan. 20]; 19(1): 50-62. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1360273/

Hammer KA, Carson CF, Riley TV. 2012. Effects of Melaleuca alternifolia (Tea Tree) Essential Oil and the Major Monoterpene Component Terpinen-4-ol on the Development of Single- and Mulistep Antibiotic Resistance and Antimicrobial Susceptibility. Antimicrobial Agents and Chemotherapy [Internet]. [cited 2017 Jan. 14]; 56(2): 909-915. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3264233/

Melaleuca Inc. About Melaleuca [Internet]. [cited 2017 Jan. 25]. http://www.melaleuca.com/about/melaleuca

Oil of Melaleuca, terpinen-4-ol type (Tea Tree oil). International Organization for Standardization. [cited 2017 Jan 16]; ISO 4730:2004. 

Organic Facts. 10 Incredible Benefits of Cajuput Essential Oil [Internet]. Organic Information Services Pvt. Ltd. [cited 2017 March 6]. https://www.organicfacts.net/health-benefits/essential-oils/benefits-of-cajuput-essential-oil.html

Organic Facts. 13 Surprising Benefits of Niaouli Essential Oil [Internet]. Organic Information Services Pvt. Ltd. [cited 2017 March 6]. https://www.organicfacts.net/health-benefits/essential-oils/health-benefits-of-niaouli-essential-oil.html

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Thomsen NA, Hammer KA, Riley TV, Van Belkum A, Carson CF. 2013. Effect of habituation to tea tree (Melaleuca alternifolia) oil on the subsequent susceptibility of Staphylococcus spp. to antimicrobials, trclosan, tea tree oil, terpinen-4-ol and carvacol. International Journal of Antmicrobial Agents [Internet]. [cited 2017 Jan. 25]; 41(4): 343-351. http://dx.doi.org.evergreen.idm.oclc.org/10.1016/j.ijantimicag.2012.12.011

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