Novel method to observe subtle structural modulation of stratum corneum on applying chemical agents

In the development of functional chemicals such as percutaneous penetration enhancers and cosmetics, the structural evidence at the molecular level in stratum corneum (SC) is highly desirable. We developed a method to observe a minute structural change of intercellular lipid matrix and corneocytes on applying the chemicals to the SC using synchrotron X-ray diffraction technique. The performance of the present method was demonstrated by applying typical chemicals, chloroform/methanol mixture, hydrophilic ethanol and hydrophobic d-limonene. From the small- and wide-angle X-ray diffraction we obtained the following results: on applying chloroform/methanol mixture the intercellular lipids were extracted markedly, on applying ethanol the intercellular lipid structure was slightly disrupted, ethanol molecules were taken into the corneocytes and in addition the pools of ethanol seem to be formed in the hydrophilic region of the intercellular lipid matrix in the SC, and on applying d-limonene the repeat distance of the long lamellar structure increased by incorporating d-limonene molecules, the intercellular lipid structure was slightly disrupted, and the pools of d-limonene were formed in the hydrophobic region of the intercellular lipid matrix in the SC.