Percutaneous absorption of sunscreens from liquid crystalline phases

The purpose of the present study was to investigate the effects of two noni onic surfactants with liquid crystalline structures on the cutaneous availa bility of two sunscreens. Three liquid crystalline structures were investig ated: lamellar, hexagonal and cubic. The diffusion of sunscreens within the liquid crystals was determined by measuring transport kinetics into an unl oaded surfactant medium from a similar system loaded with the sunscreens. T he diffusion coefficients were the greatest in the cubic systems for benzop henone-4 (a hydrosoluble sunscreen) and in lamellar systems for octyl metho xycinnamate (a liposoluble sunscreen). So the diffusion in this surfactant systems was strongly dependent on the structure of the liquid crystal and o n the physicochemical properties of the solute. The transcutaneous fluxes w ere determined using a Franz-type diffusion cell. The liquid crystalline ve hicles modified the transcutaneous fluxes of benzophenone-4 but did not cha nge those of octyl methoxycinnamate. The solute diffusion within the vehicl e was not the rate-determining step for transcutaneous permeation for eithe r sunscreen. The diffusion of benzopenone-4, within the stratum corneum and that of octyl methoxycinnamate within the dermis could be the rate-determi ning steps for their transcutaneous permeation. These two steps could be af fected differently by nonionic surfactant vehicles. (C) 1999 Elsevier Scien ce B.V. All rights reserved.