Alteration of the Structure of Human Stratum Corneum Facilitates Transdermal Delivery

Transdermal transport of pharmacologically active components into the skin depends on the ability of galenic formulations to overcome the stratum corneum (SC) barrier. Microemulsions (ME) are thermodynamically stable liquid systems composed of water, oil and surfactants which may be used for skin permeation and enhance penetration of hydrophobic as well as hydrophilic compounds. We investigated using transmission electron microscopy the effect of ME on human epidermis ex vivo, in order to establish relationship between the type of ME, i.e.: oil-in-water, water-in-oil, gellike, thickened or not with colloidal silica, and the ultrastructural changes in SC barrier resulting from their topical application. ME induced various degrees of dissociation of the SC. The intercellular lipid matrix in the SC became disorganized, which contributed to the separation of corneocytes. This effect was intensified with the increasing oil content in the ME and also when ME were applied under occlusion. The observed morphological changes were in agreement with the increased permeability of ME-treated skin to both lipophilic and hydrophilic compounds reported in the literature. Severe deterioration of the SC barrier induced with the selected ME makes them suitable for selected indications only.