Predominant adsorption of sesquiterpene constituents of lavender, tea tree, lemongrass and thyme thymol oils on hairless mouse and human hairs in an aromatic bath

Adsorption of the major constituents of lavender, tea tree, lemongrass and thyme thymol essential oils on hairless mouse skin was determined in an aromatic bath. Adsorption occurred in a concentration-dependent manner. Sesquiterpene hydrocarbons showed the most dominant adsorption, especially in dilute solution. This was followed by the hydrophobic monoterpene hydrocarbon and ester. The relatively hydrophilic monoterpene alcohol, phenol and aldehyde constituents were poorly adsorbed. The same tendency was observed on hairy mice, mouse hairs, guinea pig hairs and human hairs. This selective adsorption of sesquiterpenes was not observed on natural rubber but observed on keratin, a major protein forming skin and hairs. When examined using the authentic compounds, the sesquiterpene hydrocarbon (β-caryophyllene) and the sesquiterpenols (farnesol, nerolidol, and bisabolol) exhibited the highest adsorption, while the monoterpene limonene and linalyl acetate showed moderate adsorption, and the monoterpenic camphor, linalool, perillaldehyde, and thymol showed low adsorption. Human hairs were suggested to be an alternative to mouse skin for adsorption studies of essential oils.