Skin disposition of d-camphor and l-menthol alone and together.

The terpenes camphor and menthol are often used in topical preparations, although some data indicate concern about their skin penetration after application in most commonly used vehicles. The cutaneous disposition of these substances applied alone and together in either an oily solution or a hydrogel was evaluated ex vivo using full human skin mounted in flow-through diffusion cells. After 0.5, 1 and 2 h of application, the skin was progressively tape-stripped into three fractions of stratum corneum (SC) and the remaining epidermis with the dermis. The content of terpenes in the skin layers was determined using gas chromatography. Different penetration into the skin layers was observed depending on the type of vehicle. The highest SC absorption was noted when terpenes were applied in hydrogel, where the total content in the SC was 200 microg/cm2 for camphor and 400 microg/cm2 for menthol, and the total skin absorption was 310 and 460 microg/cm2, respectively. The SC penetration of both terpenes from the oily solution was the same (approximately equal to 35 microg/cm2). When both terpenes were present in the hydrogel the SC absorption decreased, the amounts of camphor and menthol in the SC being 50 and 190 microg/cm2, respectively (total skin accumulation was 120 and 220 microg/cm2, respectively). Such an effect was not observed for the oily solution.