Abstract: The interaction of eucalyptus oil (EO) with skin lipid liquid crystals wasinvestigated by polarizing microscopy, DSC and X-ray diffraction. Two liquid crystals of model skinlipid were prepared. The liquid crystal l (matrix l) consisted of 5 fatty acids of stratum comeumwhile liquid crystal 2 (matrix 2) consisted of cholesterol together with 5 fatty acids. Lamellarstructure was formed in the matrix 1 and matrix 2 showed lamellar structure with maltese crosses.On the addition of EO to both liquid crystals, it was observed that small amount of EO partitioninginto the liquid crystaline structure caused dispersion and swelling of lamellar structure, while largeamount of EO resulted in the breakage and disappearance, but the EO did not promote the formation of any other structures. The interaction may be one of the explanations for the increasing permeationof drugs through stratum corneum in the presence of EO and similar penetration enhancers.

Key words: Eucalrptus oil, Model stratum corneum lipids, Liquid crystals, Lamellar structure, Polarizing microscopy, Differential scanning calorimetry, X-ray diffraction