Skin barrier structure and function: The single gel phase model

A new model for the structure and function of the mammalian skin barrier is postulated. It is proposed that the skin barrier, i.e., the intercellular lipid within the stratum corneum, exists as a single and coherent lamellar gel phase. This membrane structure is stabilized by the very particular lip id composition and lipid chain length distributions of the stratum corneum intercellular space and has virtually no phase boundaries. The intact, i.e. , unperturbed, single and coherent lamellar gel phase is proposed to be mai nly located at the lower half of stratum corneum. Further up, crystalline s egregation and phase separation may occur as a result of the desquamation p rocess. The single gel phase model differs significantly from earlier model s in that it predicts that no phase separation, neither between liquid crys talline and gel phases nor between different crystalline phases with hexago nal and orthorhombic chain packing, respectively, is present in the unpertu rbed barrier structure. The new skin barrier model may explain: (i) the mea sured water permeability of stratum corneum; (ii) the particular lipid comp osition of the stratum corneum intercellular space; (iii) the absence of sw elling of the stratum corneum intercellular lipid matrix upon hydration; an d (iv) the simultaneous presence of hexagonal and orthorhombic hydrocarbon chain packing of the stratum corneum intercellular lipid matrix at physiolo gic temperatures. Further, the new model is consistent with skin barrier fo rmation according to the membrane folding model of Norlen (2001). This new theoretical model could fully account for the extraordinary barrier capacit y of mammalian skin and is hereafter referred to as the single gel phase mo del.