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Antiviral Activity of Tea Tree Oil - In vitro and in vivo

by Dr Christine F. Carson, Ms Lynn Ashton, Ms Linda Dry, Dr David W. Smith and Prof Thomas V. Riley

 

RIRDC Publication No 05/130     RIRDC Project No UWA-40A

Executive Summary
Tea tree oil (TTO) is a popular ingredient in many cosmetic and medicinal products in Australia. Few regulatory dictates apply to ingredients for cosmetic products in Australia except that they must be safe. Since TTO is considered safe in Australia and enjoys enormous popularity with the general population, it has been incorporated into a vast array of cosmetic, non-therapeutic products. In contrast, regulatory requirements for medicinal products dictate that in addition to being safe, therapeutic claims must be supported by evidence. The level of evidence required has increased over the last few decades and still varies depending on the claims being made. In recent years, the TTO industry has endeavoured to continue making therapeutic claims for TTO that were acceptable in the past and in some cases, to make greater claims. In the contemporary national and international regulatory environment, only claims that are supported by scientific data are sustainable.

Substantial progress has been made with regard to the antibacterial and antifungal properties of TTO. Significant characterisation of the spectrum, degree and mechanism of antibacterial and antifungal activity has been conducted and reported in the scientific literature. These data have formed the basis of preliminary clinical studies with several reporting promising results.

In contrast, there have been very little data available on the antiviral activity of TTO. The work described here is the first attempt to address this deficiency and shows that TTO has significant antiviral activity against herpes simplex viruses. This antiviral activity appears to be largely confined to a direct effect on the extracellular virus particle, prior to penetration into a host cell. No significant antiviral activity could be detected once virus had entered cells or after pre-exposing cells to TTO prior to infection. Several of the components of TTO were tested and shown to have antiviral activity. Terpinen-4-ol, ?-terpineol and 1, 8-cineole appeared slightly more active in vitro than whole oil, although the differences may not be clinically significant. ?-Cymene and ?- and ?-terpinene did not exhibit significant antiviral activity in this model, however, but the possibility that these and other components may contribute to the overall activity of the oil should not be disregarded.

Proof of the in vitro antiviral activity of TTO opens up the possibility that TTO may be a potentially useful topical treatment for cutaneous viral infections such as cold sores, caused by HSV. Since there was no data on this subject, a preliminary investigation was undertaken in the form of a pilot study. Twenty patients suffering from an episode of cold sores, also known as recurrent herpes labialis, were recruited and randomised to receive 6% tea tree oil ointment or placebo (no active ingredient) ointment. Patients' cold sores were assessed daily and a swab of the cold sore was also taken daily. The presence or absence of herpes simplex virus in the cold sore was determined by two methods. These were culture (to detect viable virus) and polymerase chain reaction (PCR) to detect viral DNA.

One patient in the TTO group was withdrawn from the study due to an adverse reaction to the ointment. No herpes virus was detected in specimens from the site of this patient's suspected lesion and no cold sore developed. Another patient, randomised to the placebo group, failed to attend any visits after the first one. These two patients were excluded from the analysis.

Results from the remaining 18 patients were analysed. For the nine patients that received the TTO ointment, the median number of days taken for the cold sore to heal completely was 9.

For the nine patients that received the placebo ointment, the median number of days to healing was 12.5. The median number of days of culture positivity in the TTO group was 3 while in the placebo group it was 4. However, the median number of days on which viral DNA could be detected by the PCR test was 6 in both groups. The median number of days to crust was also the same in both treatment groups and was 4. Of the two methods used to detect herpes virus, the PCR test detected virus for 3-4 days longer than the culture test.

However, the PCR test only detects virus in terms of presence/absence. The culture method allows the number of virus particles present to be estimated. Results from this pilot study suggest that the number of virus particles present in cold sores treated with TTO ointment is lower than in those treated with the placebo ointment. All of these outcomes suggest that TTO ointment speeds the healing of cold sores although none of them was statistically significant.

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