All of the previous assessments of tea tree oil have been acquired from animal and human testing. Just recently, however, cytotoxic testing of the oil has been carried out. The use of cytotoxic (toxic to cell tissue) in vitro (test tube) testing has made testing of substances that are quite toxic, more animal friendly and thus more acceptable. The other advantage is that the same tissues can be used to test many substances and provide a more accurate comparison of the relative toxicity of different substances. This approach is also being used for predictive testing for potential allergens (Krasteva et al. 1996). According to Soderberg et al. (1996), tea tree oil when tested at 100,ag/ml had a cytotoxic effect on epithelial and fibroblast cells for only the first hour of a 24 hour test duration.
More recently, Hayes et al. (1997) investigated tea tree oil cytotoxicity with respect to the major oxygenated monoterpenoid constituents terpinen-4-ol, 1,8-cineole and a-terpineol. The oil tested contained terpinen-4-ol 40%, 1,8-cineole 4%, a-terpineol 4% and results showed that a-terpineol>tea tree oil>terpinen-4-ol>cineole for overall cytotoxicity. When tea tree oil was compared with controls mercuric chloride (highly toxic) and aspirin (very low toxicity) on the same cell types (liver, skin, lymph and bone marrow), ratings were mercuric chloride>tea tree oil>aspirin. The authors state that these cytotoxicity results support the use of tea tree oil in topical applications but not for ingestion purposes.
CINEOLE AND OTHER MELALEUCA SPECIES' OILS
According to Tisserand and Balacs (1995), 1,8-cineole is non-toxic, non-irritant and non-sensitising. This being the case, one would expect that high cineole content oils would be similar. However, as mentioned earlier, eucalyptus oil, although fitting into this category, is still regarded as potentially dangerous to small children.
Commercial cajuput oil, presumably the "cajeput" (Melaleuca leucadendron) of Tisserand and Balacs (1995) and now known as Melaleuca cajuputi (see Chapter 14), is normally a high cineole (50-60%) oil. Tisserand and Balacs (1995) state that this "cajeput" oil has an LD50 between 2-5g/kg, is non-irritant and has negligible risk of skin sensitivity.
Niaouli oil, from Melaleuca quinquenervia, also a cineole type oil, has been assessed by Aboutabl et al. (1996) using ethanol extracts as having an LD50 of 147.5mg/kg while
Tisserand and Balacs (1995) indicate that niaouli oil is safe to be used in aromatherapy and is considered non-irritant and non-sensitizing. Linalool and nerolidol, the major constituents in some chemotypes of Melaleuca quinquenervia, are also considered to be safe for aromatherapy use (Tisserand and Balacs 1995) and hence non-irritant and non-sensitising (see Chapter 15).
The only Melaleuca oil that is currently considered as a potential carcinogen is the oil of Melaleuca bracteata which contains approximately 80% methyl eugenol. According to Randerath et al. (1984) and Tisserand and Balacs (1995) this oil should be avoided as currently the oil is considered carcinogenic to rodents. Until such time as it is assessed as non-carcinogenic to humans, this advice should be heeded.
Although not unduly toxic when ingested, tea tree should continue to be used mainly for topical applications. It would appear that tea tree oil (Melaleuca alterntfolia) is non-irritating even when used up to 10% (Altman 1991) or 25% (Southwell et al. 1997) on unabraded healthy skin. It is not recommended that it be used on sensitive, dermatitis affected or abraded skin for extended periods. Some people do become sensitized to tea tree oil on rare occasions especially those that have a history of allergic responses. Generally, however, as there was little irritation or sensitization with tea tree oil in formulations up to 25%, products of that concentration or less are recommended.
Aboutabl, E.A., Abdelhakim, G. and Moharram, F.A. (1996) A study of some pharmacodynamic actions of certain Melaleuca species grown in Egypt. Phytotherapy Research, 10(4), 345-347. Altman, P. (1991) Assessment of the skin sensitivity and irritation potential of tea tree oil. Pharmaco
Pty Ltd., Sydney, Australia. Apted, J.H. (1991) Contact dermatitis associated with the use of tea tree oil. Australas. J. Dermatology, 32, 177.
Austteam, (ca. 1995) Technical & Material Safety Data Sheet—Tea Tree Oil, Austteam, Lismore, Australia.
Bolt, A.G. (1989a) Acute dermal irritation of tea tree oil in the rabbit. 13th January. Report for the Australian Tea Tree Industries Association. Pharmaceutical Consulting Services, Lindfield, Sydney. Bolt, A.G. (1989b) Skin sensitization potential of tea tree oil in the rabbit. 13th January. Report for the Australian Tea Tree Industries Association. Pharmaceutical Consulting Services, Lindfield, Sydney. Bolt, A.G. (1989c) Acute dermal toxicity limit test of tea tree oil in the rabbit. 20th February. Report for the Australian Tea Tree Industries Association, Pharmaceutical Consulting Services, Lindfield, Sydney.
Bolt, A.G. (1989d) Acute oral toxicity of tea tree oil in the rat. 24th April. Report for theAustralian Tea
Tree Industries Association. Pharmaceutical Consulting Services, Lindfield, Sydney. Bolt, A.G. (1989e) Skin sensitisation potential of tea tree oil in the guinea pig. 13th January. Report for the Australian Tea Tree Industries Association. Pharmaceutical Consulting Services, Lindfield, Sydney.
Carson, C.F, and Riley, T.V. (1995) Toxicity of the essential oil of Melaleuca alternifolia or tea tree oil
Journal of Toxicology—Clinical Toxicology, 33(2), 264-269. De Groot, A, and Weyland, W. (1992) Systemic contact dermatitis from tea tree oil. Contact Dermatitis, 27, 279-280.
De Groot, A. and Weyland, W. (1993) Contact allergy to tea tree oil. Contact Dermatitis, 26, 309.
Del Baccaro, M.A. (1995) Melaleuca oil poisoning in a 17-month-old. Vet. and Human Toxicology, 37(6), 557-558.
Elliot, C. (1993) Tea tree oil poisoning [Letter]. The Medical Journal of Australia, 159, 830-831.
Ford, R. (1988) Fragrance raw materials monographs. Food Cosmet. Toxicology, 26, 407.
Gurr, F.W. and Scroggie, J.G. (1965) Eucalyptus oil poisoning treated by dialysis and mannitol infusion. Australian Annals of Medicine, 14, 238-249.
Hayes, A.J., Leach, D.N. and Markham, J.L. (1997) In vitro cytotoxicity of Australian tea tree oil using human cell lines. J. Essent. Oil Res., 9, 575-582.
International Standards Organization (1996) Oil of Melaleuca, terpinen-4-ol type (Tea Tree Oil). International Standard ISO 4730:1996(E), International Standards Organization, Geneva.
Jacobs, M.R. and Hornfeldt, M.S. (1994) Melaleuca oil poisoning. Clinical Toxicology, 32(4), 461464.
Knight, T.E. and Hausen, B.M. (1994) Melaleuca oil (tea tree oil) dermatitis. J. Am. Acad. Dermatol., 30, 423-7.
Krasteva, M., Peuget-navarro, J., Moulon, C., Courtellemont, R, Redziniak, G. and Schmitt, D. (1996) In vitro primary sensitization of hapten-specific T cells by cultured human epidermal Langerhans cells-a screening predictive assay for contact sensitizers. Clinical and Experimental Allergy, 26, 563-570.
Lassak, E.V. and McCarthy, T. (1983) Australian Medicinal Plants, Methuen Sydney, Australia, p. 97.
Magnusson, H.C. and Kligman, A.M. (1969) The identification of contact allergens by animal assay. The guinea pig maximization test. J. Invest. Dermatol., 52, 268-276.
Main Camp Tea Tree Oil Group Newsletter (1998), Tea Tree Oil News, 1, 3.
Moss, A. (1994) Tea tree oil poisoning [Letter]. The Medical Journal of Australia, 160, 236.
Opdyke, D.L.J. (1975a) Fragrance raw materials monographs (limonene). Food and Cosmetics Toxicology, 13, 825-826.
Opdyke, D.L.J. (1975b) Fragrance raw materials monographs (eucalyptol). Food and Cosmetics Toxicology, 13, 105-106.
Opdyke, D.L.J. (1977) Fragrance raw materials monographs (methyl salicylate). Food and Cosmetics Toxicology, 15.
Phillips, L., Steinberg, M., Maibach, H.I. and Akers, W.A. (1972) A comparison of rabbit and human skin responses to certain irritants. Toxicology and Applied Pharmacology, 21, 369-382.
Randerath, K., Haglund, R., Phillips, D. and Vijayaraj Reddy, M. (1984) 32P-Post-labelling analysis of DNA adducts formed in livers of animals treated with safrole, estragole and other naturally-ocurring alkenylbenzenes 1. Adult female CD-1 mice. Carcinogensis, 5(12), 1613-1622.
Rural Industries Research and Development Corporation (1996) Acute dermal irritation/corrosion of 75%, 50%, 25%, and 12.5% tea tree oil solutions in the rabbit . Pharmatox Project Report, T1836.A, p. 7.
Schaller, M.S. and Korting, H.C. (1995) Allergic airborne contact dermatitis from essential oils used in aromatherapy. Clin. & Exp. Dermatology, 20, 143-145.
Seawright, A. (1993) Tea tree oil poisoning—comment [Letter]. The Medical Journal of Australia, 159, 831.
Selvaag, E., Eriksen, B. and Thune, P. (1994) Contact allergy due to tea tree oil and cross-sensitization to colophony. Contact Dermatitis, 31, 124-125.
Smith, A. and Margolis, G. (1954) Camphor poisoning. American Journal of Pathology, 30, 857-869.
Soderberg, T., Johansson, A. and Gref, R. (1996) Toxic effects of some conifer resin acids and tea tree oil on human epithelial and fibroblast cells. Toxicology, 107, 99-109.
Southwell, I.A., Freeman, S. and Rubel, D. (1997) Skin irritancy of tea tree oil. J. Essen. Oil Res., 9, 47-52.
Stevenson, C.S. (1937) Oil of wintergreen (Methyl salicylate) poisoning. J. Med. Sc., 193, 772-788.
Tea Tree Oil Growers of Australia (ca. 1989) Australian Tea Tree Oil Toxicology Data, Data Sheet 5, Tea Tree Oil Growers of Australia, Grafton, Australia.
Tisserand, R. and Balacs, T. (1995) Essential Oil Safety—A Guide for Health Care Professionals,
Churchill Livingstone, Edinburgh, pp. 45-55, 80, 82, 150, 187, 204, 219. Van der Valk, P.G.M., De Groot, A.C., Bruynzeel, D.P., Coenraads P.J. en Weijland, J.W. (1994)
Allergisch contacteczeem voor 'tea tree'-olie. Ned Tijdschr Geneeskd, 138(16), 823-825. Villar, D., Knight, M.J., Hanson, S.R. and Buck, W.B. (1994) Toxicity of Melaleuca Oil and Related Essential Oils Applied Topically on Dogs and Cats. Vet. Human toxicology, 36(2), 139-142.
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