Bacterial Infections of the Skin

A number of infections of the hair follicles and sebaceous glands, such as pimples, acne vulgaris and furunculosis (boils and abcesses) are caused by bacteria, including S. aureus, Streptococcus spp. and Propionibacterium acnes. These organisms are sensitive to tea tree oil in laboratory tests (see previous sections) and there have been a number of studies carried out to determine their efficacy in clinical situations.

Feinblatt (1960) discusses the unique property of oils containing terpene derivatives of benzene of penetrating to the subcutaneous layers by mixing with sebaceous secretions and reports the use of such an oil in the treatment of 25 cases of furunculosis (boils). Undiluted 'cajeput-type' oil from Melaleuca alternifolia was used to paint the infected area two to three times daily, and patients were examined on alternate days. The study included ten untreated controls: five of the controls had similar symptoms at the end of the eight-day study, while the boils of five worsened and were finally incised. Only one of the twenty-five patients treated with the Melaleuca oil required incision, and in 15 cases the boil site had completely cleared in eight days. A reduction in symptoms was recorded for the remaining nine participants. Three patients reported slight temporary stinging following application of the oil, but no toxic effects were reported.

Whilst this study provides evidence of the efficacy of tea tree oil in the treatment of furunculosis, the author does not specify the chemical composition of the oil used and it is possible that the oil was a high cineole (eucalyptol) variety. This highlights the importance of specifying the chemical composition of oils used in all studies if comparisons are to be drawn between them, or if the work is to support applications for registration of oils or products containing them.

BĂ©laiche (1985b) reports the efficacy of the oil in the treatment of two cases of impetigo (one caused by Staphylococcus and the other by Streptococcus) and three cases of acne caused by Staphylococcus spp. Improvement was reported in all cases, but the lack of untreated controls and the small numbers limit the conclusions which can be drawn. In addition, the test oil does not meet the specification of the current ISO standard because of the high concentration of p-cymene (16.4%).

A more rigorous study was carried out by Bassett et al. (1990) to examine the efficacy of a tea tree oil preparation in the treatment of acne vulgaris, a multifactorial disorder, common especially among teenagers. The bacterium, Propionibacterium acnes, which has been implicated as one of the causative factors, is sensitive to tea tree oil in in vitro tests (Table 2). Bassett et al. (1990) report MIC values of 0.75% or less for 90% of strains tested, while Carson and Riley (1994) report lower values. As a result, the oil has been incorporated in a number of commercially available facewash and pimple gel preparations, generally at concentrations in the range of 0.5-4.0% (w/w or w/v).

Bassett et al. (1990) report the results of a single-blind, randomised clinical trial on 124 patients with mild to moderate acne. The efficacy of a 5% tea-tree oil gel was compared to a 5% benzoyl peroxide lotion in terms of its ability to reduce the number of inflamed and non-inflamed lesions over the three-month treatment period. Oiliness, erythema, scaling, pruritis and dryness were also assessed as a measure of skin tolerance.

The results showed that the number of both inflamed and non-inflamed lesions was significantly reduced in both groups, with benzoyl peroxide having a more rapid onset of action. Benzoyl peroxide was significantly more effective than tea-tree oil in reducing inflamed lesions (P<0.001 at three months); however, there was, no significant difference between the two protocols in the reduction of non-inflamed lesions. Of the two preparations, tea tree oil was better tolerated than benzoyl peroxide, with fewer reports of side-effects such as skin scaling, pruritis and dryness.

The above study has been criticised because of the lack of a control or placebo group to which the test groups can be compared, and further trials, including a placebo group are needed to confirm the findings of the study. The study was considered single-blind by the authors, because, although neither group was informed of the preparation being used, it was reported that it was not possible to disguise the characteristic smell of tea tree oil. This will remain an issue in all future clinical trials of products containing tea tree oil as the active ingredient.

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