Executive Summary
Headlines in Europe recently stated: “tea tree oil – unsafe and unstable”. This undesirable media coverage overseas came as a challenge to the Australian tea tree oil industry at a time when attempts to combat low prices by better market promotion of the oil were gaining momentum. The headlines followed the release of a European SCCP (Scientific Committee on Consumer Products) opinion that concluded that insufficient data were available on the safety and stability of the oil.

Consumers and the media need to know the facts about the safety and stability of tea tree oil that, along with proven efficacy, have made the oil such a popular health care product over the last 70 years. The industry is addressing this situation by commissioning approved tests in order to obtain a more complete safety dossier on tea tree oil.

For this to be achieved, the oils tested must be well defined chemically for the dossier to be valid.

This investigation outlines how, from eleven commercial samples screened, three oils (one fresh, one oxidised and one, blended from commercial oils, mildly oxidised) were chosen by peroxide index determination. These samples were then thoroughly defined by GC, GCMS and physical constants to determine status with respect to the ISO standard for tea tree oil before being recommended for dermal penetration and other safety parameter investigations for the dossier. The methods used were internationally accepted procedures for determining peroxide value (British or European Pharmacopoeia methods), GC profiles and physical constants (ISO Standard) and GCMS (generally accepted literature procedures).

From 11 tea tree oils screened, three samples with sufficient bulk were selected for safety parameter testing. These were found to display mean peroxide values of 1.1, 11.7 and 30.5 milliequivalents of active oxygen per kg. The first of these was the only sample within the limits of the Australian and International Standards for tea tree oil. The oxidised oil failed to satisfy these standards at the following points: in the chromatographic profile, p-cymene levels were high and ?- and ?-terpinene levels low even though other constituents were within the ISO Standard limits. The partially oxidised oil failed to meet the standard at p-cymene content and relative density.

As a result of this investigation, it is suggested that oxidised tea tree oils are usually, but not always, seen to be associated with high peroxide values and high p-cymene contents. Of the 11 samples screened, one with low peroxide value, showed high p-cymene content and conversely, one with high peroxide value was low in p-cymene. The oxidised oil provides an oil that would simulate an oil from a bottle which had been frequently opened for use by the consumer and inadvertently let deteriorate.

The testing planned for the selected oils will be of economic benefit as a better defined oil will lead to more sales and be of social benefit as the safety and stability of the oil become recognised.
 

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