During the last ten years, sales of essential oil from the Australian tea tree (Melaleuca alternifolia) have increased from around 8 tons to 150-200 tonnes per annum. Many buyers consider 1,8-cineole (eucalyptol) concentration to be the most important quality criterion for their purchases. The available data does not support the view that low cineole (0-5%) tea tree oils are superior to moderate cineole (5-15%) oils. This paper evaluates the claims about cineole in tea tree oil and reviews the results of recent skin irritancy and bioactivity investigations which show that cineole is neither an irritant nor an antagonist. Reasons for this industry misconception are suggested.
Previous literature: One year after being raised to species rank from Melaleuca linarifolia var. alternifolia, M. alternifolia essential oil was investigated and reported to contain 6-8% 1,8-cineole. The existence of chemical varieties with a higher concentration of cineole (termed “physiological forms”) soon became evident, prompting investigations which established three varieties based on cineole content: Type (6-14%), Var. A (31-41%) and Var. B (54-64%). It must be remembered that these cineole determinations were based on o-cresol methods. With the advent of gas chromatography (GC) and the analysis of statistically significant numbers of samples, these varieties tended to merge as cineole concentrations of 0.5-86.3% were discovered. The GC analysis of thousands of samples, first at the Museum of Applied Arts and Sciences, and then at NSW agriculture laboratories (the Biological and Chemical Research Institute and the Wollongbar Agricultural Institute), indicated that cineole concentration was inversely propmtional to terpinen-4-ol concentration. Hence, as cineole concentration increases, terpinen-4-01 concentration decreases.