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Lamellar structure of intercellular lipids in stratum corneum is considered to be the essential physical barrier to protect living body from dehydration, invasion of hazards and permeation of compounds. The intercellular lipid of the human stratum corneum form a long period lamellar of about 13 nm and a short period lamellar of about 6 nm, and hexagonal and orthorhombic are known as a packing structure. To observe those structure, synchrotron X-ray diffraction is considered to be powerful tool. There observed phase transition of liquidation of orthorhombic packing (~40 ℃), solubilization of long lamellar and high-temperature hexagonal (~50 ℃), liquidation of short lamellar (~70 ℃) and solubilization of high-temperature hexagonal (~80 ℃). These structural changes are thought to be closely related to the barrier function of the skin. When menthol was administered to skin surface, the nanostructure of the intercellular lipids became liquid crystal. That is, the permeability of the substance was related to the rigidness of the lamellar structure. Furthermore, in experiments with lipid models using typical intercellular lipids, the mode of action could be different depending on the stereo activity of menthol. Liquid crystallization of the lamellar structure is one way to alleviate the barrier function of the skin. Therefore, by devising the components and mixing ratio of the transdermal/cosmetic formulation, it becomes possible for development of effective formulation.
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