Melaleuca alternifolia essential oil (Tea Tree Oil, TTO) is well-known for its several biological activities [1],[2] and it is largely used as ingredient in skin care products.
The aim of this study is the quantitative evaluation on the permeation, skin-layers distribution (stratum corneum, epidermis and dermis) and release in the surrounding environment of TTO markers (i. e. -pinene, β-pinene, α-terpinene, 1,8-cineole, γ-terpinene, 4-terpineol, α-terpineol) when applying a 5 % TTO cream at a finite dosing regimen. Permeation kinetics were studied in vitro on pig ear skin using conventional and ad hoc (for evaluation of released compound in the surrounding environment) static glass Franz diffusion cells. Formulation, receptor phases and skin-layers were analyzed by adopting a fully-automatized and solvent-free analytical method using Headspace Solid Phase Microextraction (HS-SPME) combined with Gas Chromatography-Mass Spectrometry (GC–MS).
Skin-layers overall contained less than 1 % of each TTO marker. Only oxygenated terpenes (i. e. 4-terpineol, α-terpineol and 1,8 cineole) significantly permeated through the skin layers, while hydrocarbons were found at trace level in the receptor phase. As expected, due to the volatility of TTO markers, a substantial fraction of each TTO component applied on the skin was released in the surrounding environment.
To the best of the authors’ knowledge, in this work for the first time 1) a completely solvent-free approach is used to quantify the TTO markers from skin layers, and 2) an ad hoc modified static Franz cells is used to quantify the release of TTO components in the surrounding environment.
