AromaChemistry and Applications of Tea Tree Oil – Part 3 of 4

Potential Uses For Humans

In vitro studies have shown great potential for Tea Tree Oil as a therapeutic agent, but few in vivo studies have been conducted. Tea Tree Oil has been commonly used for acne, dandruff, cuts, as well as other conditions (10, 11). In vivo research is currently reviewing and determining the efficacy for the aforementioned treatment options, in addition to potential new uses, including countering inflammation. The studies that have been conducted provide insight on the potential incorporation of TTO as a mainstream natural medicine (12, 13).

Satchel et al conducted a single-blind study to assess the efficacy and tolerability of 5% tea tree oil shampoo in the treatment of dandruff, compared to placebo. The study involved 126 subjects with mild to moderate dandruff; patients with severe and unstable dandruff were not permitted. After an initial two-week period in which all individuals used the same shampoo, subjects were asked to shampoo their hair daily and let shampoo remain 3 minutes before rinsing.  After 2 and 4 weeks, subjects were reevaluated using the whole scalp lesion score (11).

With this scoring, the scalp was divided into quadrants, and each quadrant was measured for numerous characteristics. Assessments were performed on total area and severity, and the product of these two variables calculated a comparative value of “whole scalp lesion score.” The area of involvement was measured on a scale of 1 to 5 for each quadrant, with 1 = 10% involvement and with 5 = more than 70% involvement. Furthermore, severity was measured on a scale of 0 to 3, with 0 for normal skin and 3 indicating erythema with numerous yellowish-white scales. Additionally, subjective assessments of scaliness, itchiness, and greasiness were administered. These factors were assessed on a 10-cm linear analogue scale. In this situation, the first extreme, 0 cm, indicated no affliction, whereas 10 cm indicated “worst ever (11).”

Significant improvements were seen in all of the criteria, although only scaliness was statistically insignificant (Tables 4 & 5). Additionally, no severe adverse events were mentioned, and fewer events were recorded, in general, for the Tea Tree Oil group. Some individuals in this group did complain of mild stinging in the eyes and mild burning or itching of scalp (11).

Table 4.

Comparison of 5% TTO and Placebo on Whole Scalp Lesion Score (11)

Group	Assessment	Baseline	After 2 Weeks	After 4 Weeks
5% Tea Tree Oil	Whole Scalp Lesion Score	91.0	71.5	53.0
Placebo		99.7	93.0	88.2

 

Table 5.

Comparison of Improvement of 5% TTO and Placebo on Area, Severity, Itchiness, Greasiness, and Scaliness (11)

Assessment	Improvement in Placebo (%)	Improvement in 5% Tea Tree Oil (%)
Total Area Score	12.5	28.3
Total Severity Score	2.8	23.4
Itchiness	12.1	23.0
Greasiness	8.2	25.9
Scaliness	16.9*	25.6*

*Not statistically significant difference

In accordance with relevant in vitro studies, this study suggests that Tea Tree Oil may play a role in relieving dandruff and its side effects. It appears that it is not only an effective treatment but is also well tolerated. Fewer subjects suffered adverse events in the Tea Tree Oil group, compared to the placebo group, and those that did had only mild reactions (11).

Tea Tree Oil and its anti-inflammatory activity is not so commonly recognized nor understood. A study conducted by Koh et al observed the effects of Tea Tree Oil on histamine-induced inflammation. Histamine is the main mediator for allergen-induced weal and flare responses. Also associated with the effects of histamine include reddening of the skin and plasma extravasation (11).

In this study, the control group of 5 females and 1 male was treated with 25 μL liquid paraffin. The experimental group was treated with 25 μL undiluted TTO and included 16 females and 5 males. All subjects were injected intradermally with histamine (50 μL of a 100 μg/mL solution) into the inner forearm of both arms.  However, only one arm was treated topically with TTO or paraffin wax, thereby enabling a basis for comparison. Weal and flare were measured every 10 minutes for 60 minutes. A weal is a tissue oedema, and a flare is a wider spread erythema. After 20 minutes, the treatments were administered topically; the experimental group received TTO, whereas the control group received paraffin wax. In addition, subjects were asked to grade their pruritus (itchiness). This was quantified based on a subjective scale of 0 to 3, with 0 indicating no itch, 1 indicating mild, 2 indicating moderate, and 3 indicating severe itch (11).

The results from the study indicated that mean flare area exhibited no significant differences from either the control or experimental groups throughout the experiment. Therefore, both treatments were ineffective in this capacity. The control group also displayed no significant difference in mean weal volume between the untreated arm and liquid paraffin treated arm. Not only this, but the mean weal volume actually continued to increase throughout the experiment. After 10 minutes from treatment application, only 7 of 21 subjects from the experimental group displayed an increase in the mean weal volume in the arm with TTO, compared to 17 of 21 in the arm without any treatment. At 60 minutes, TTO was statistically significantly lower than that of the arms without treatment. Additionally, there was no significant difference in the itch scores between the control and experimental groups (11).

This study suggests that Tea Tree Oil does play a part in reducing certain aspects of inflammation induced by histamine, and most specifically, the weal area. TTO was not effective at reducing the flare area or pruritus associated with the inflammation. It is believed that TTO affects one of the pathways involved in oedema formation, although the identification of which pathway is still unclear (11). It coincides with the anti-inflammatory action of TTO exhibited in mice after inhalation (12).

I.B. Basset et al carried out a study to observe the efficacy and tolerability of 5% Tea Tree Oil gel, compared to 5% benzoyl peroxide lotion, in the treatment of moderate acne. The study involved 124 subjects in a single-blind, clinical trial. TTO was supplied as a 5% water-based gel in 30 g aliquots and benzoyl peroxide was in the form of a 5% water-based lotion in 25 mL aliquots. After baseline data was collected, subjects were asked to come in on a monthly basis, for three months, to be evaluated (10).

The evaluation utilized in this study was “the counting technique,” in which all postules were counted via observation. In order to minimize error from the potential subjectivity of this type of assay, the same investigator surveyed all participants. The total number of inflamed lesions (superficial and deep), as well as non-inflamed lesions (open and closed comedones) were counted and recorded. In addition to the lesion counts, subjects were also assessed for skin tolerance, in terms of oiliness, erythema, scaling, pruritis, and dryness. Subjects were graded on the following scale: 0 – nil, 1 – mild, 2 – moderate, and 3 – severe. Subjects were also asked to report any adverse reactions or effects during the previous month’s treatment (10).

There were no significant differences in baseline assessment between the experimental and control groups, with exception of the facial erythema for which the TTO group had a greater P value (<0.05). Figure 5 shows that both treatments were effective in decreasing the mean number of inflamed lesions. Additionally, as seen in Figure 6, both treatments were also effective in decreasing the mean number of non-inflamed lesions. In both cases, the benzoyl peroxide was more effective, although TTO’s results were comparable. However, 79% of the benzoyl peroxide treatment group complained of unwanted effects, in comparison to only 44% of the TTO treatment group with reports. As the Figures 4 & 5 show, the effects were noticed after a longer period of time with TTO, but it is important to consider that the treatment was better tolerated and caused fewer incidences of adverse reactions (10).

Figure 5.

The mean number of inflamed lesions at each review for the two groups (10)

 

Figure 6.

The mean number of non-inflamed lesions at each review for the two groups (10)

The available research does confirm that TTO is relatively effective in treating conditions such as acne, dandruff, and inflammation induced by histamine (1, 11, 14). Additionally, tolerability of TTO was handled very well, and in most incidences provided for fewer and less severe adverse reactions (10, 11). However, as in the study with acne, its onset may be delayed compared to other medicinal agents (10). Due to its studied antimicrobial activity, TTO is also being considered as a possibility in wound care, as well as cuts and burns (14).

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.

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