Cutaneous absorption and elimination of three acyclic terpenes - in vitro studies

The purpose of the study was to investigate skin absorption and elimination of three acyclic terpenes: citronellol (C), linalool (L) and linalyl acetate (LA). The pure terpenes were applied onto the human skin in vitro, and after 1-4 h, their content in the stratum corneum layers and in the epidermis/dermis was determined using gas chromatography. Similarly, the amounts of terpenes in the skin were analysed during 4 h following 1-h absorption. Good absorption to the all skin layers was demonstrated as soon as after 1 h: the total skin cumulation of L, LA and C was 827, 124 and 954 mug/cm(2), respectively. A self-promoting absorption was observed for L, since the amount of this terpene analysed in the stratum corneum after 1 h was 78.3, rising to 479 mug/cm(2) after 4 h. During the elimination phase, a constant drop in the total amount in the skin was observed only for C, while the total skin content of L and LA did not change, although diffusion from the stratum corneum to epidermis/dermis occurred. The log P values of the terpenes were calculated using three different programs, but generally, neither absorption nor elimination can be directly correlated with the physicochemical parameters, despite of the fact that the least absorption was observed for the most lipophilic LA. (C) 2003 Elsevier B.V. All rights reserved.