Skin penetration of terpenes from essential oils and topical vehicles.

The purpose of this study was to evaluate the in vitro cutaneous penetration of five terpenes--linalool, linalyl acetate, terpinen-4-ol, citronellol and alpha-pinene--applied in pure essential oils or in dermatological formulations (o/w emulsion, oily solution or hydrogel) containing 0.75 % w/w of the essential oils. Different skin absorption was observed depending on the type of the vehicle and terpenes' log P values. Cutaneous accumulation of terpenes is several times higher when they are applied in pure essential oils than in topical vehicles. Penetration of terpinen-4-ol to the skin was better from an oily solution (approximately 90 microg/cm (2)) than from an emulsion (60 microg/cm (2)). No penetration of linalyl acetate from topical vehicles into viable skin was observed, but also for this terpene penetration to the upper layers of the stratum corneum was 2-times higher when an oily solution was used. In contrast, the cutaneous absorption of linalool was the same from both vehicles (50-60 microg/cm (2)). The skin penetration of alpha-pinene was not traceable when it was applied in an oily solution. Only a small amount (approximately 5 microg/cm (2)) of this terpene was determined in viable skin after application as a hydrogel. Citronellol applied in a hydrogel penetrated into all skin layers in a total amount of 25 microg/cm (2), while no penetration into viable skin layers after application of an oily solution was noted. Only citronellol permeated into the acceptor medium.