title: Human skin penetration of the major components of Australian tea tree oil applied in its pure form and as a 20% solution in vitro.
abstract: The safety of topical application of Australian tea tree Oil (TTO) is confounded by a lack of transdermal penetration data, which adequately informs opinions and recommendations. In this study we applied TTO in its pure form and as a 20% solution in ethanol in vitro to human epidermal membranes from three different donors, mounted in horizontal Franz-type diffusion cells, using normal 'in use' dosing conditions (10 mg/cm2). In addition, we examined the effect of partially occluding the application site on the penetration of TTO components. Our data showed that only a small quantity of TTO components, 1.1-1.9% and 2-4% of the applied amount following application of a 20% TTO solution and pure TTO, respectively, penetrated into or through human epidermis. The largest TTO component penetrating the skin was terpinen-4-ol. Following partial occlusion of the application site, the penetration of terpinen-4-ol increased to approximately 7% of the applied TTO. Measurement of the rate of evaporation of tea tree oil from filter paper (7.4 mg/cm2) showed that 98% of the oil evaporated in 4 hours. Overall, it is apparent that the penetration of TTO components through human skin is limited.
authors.affiliation: Therapeutics Research Unit, University of Queensland, Qld, Australia. s.cross@uq.edu.au <s.cross@uq.edu.au>
authors.forename: Sheree E
authors.initials: SE
authors.lastname: Cross
authors.forename: Michael
authors.initials: M
authors.lastname: Russell
authors.forename: Ian
authors.initials: I
authors.lastname: Southwell
authors.forename: Michael S
authors.initials: MS
authors.lastname: Roberts
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods*; D000081005:Cyclohexane Monoterpenes; D053138:Cyclohexenes / Q000737:chemistry; D004058:Diffusion; D004304:Dosage Forms; D004817:Epidermis / Q000378:metabolism; D005260:Female; D006801:Humans; D039821:Monoterpenes / Q000737:chemistry; D018570:Risk Assessment; D012867:Skin / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D012995:Solubility; D013499:Surface Properties; D020947:Tea Tree Oil / Q000008:administration & dosage*; D013678:Technology, Pharmaceutical / Q000379:methods; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors
chemical_list: D000081005:Cyclohexane Monoterpenes; D053138:Cyclohexenes; D004304:Dosage Forms; D039821:Monoterpenes; D013729:Terpenes; C016775:alpha-terpineol; C034019:terpinenol-4; D020947:Tea Tree Oil