Skin Penetration of Terpenes from Essential Oils and Topical Vehicles

Abstract

The purpose of this study was to evaluate the in vitro cutaneous penetration of five terpenes - linalool, linalyl acetate, terpinen-4-ol, citronellol and α-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 (∼90 μg/cm²) than from an emulsion (˜60 μg/cm²). 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 μg/cm²). The skin penetration of α-pinene was not traceable when it was applied in an oily solution. Only a small amount (∼5 μg/cm²) 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 μg/cm², while no penetration into viable skin layers after application of an oily solution was noted. Only citronellol permeated into the acceptor medium.

Abbreviations

C:citronellol

L:linalool

LA:linalyl acetate

αP:α-pinene

T:terpinen-4-ol

SC:stratum corneum

SC I:outer fraction of stratum corneum

SC II:middle fraction of stratum corneum

SC III:inner fraction of stratum corneum

ED:epidermis with dermis

Key words

skin penetration - essential oils - monoterpenes

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