A domain mosaic model of the skin barrier
The skin barrier primarily protects the body against uncontrolled loss of water and in addition prevents water and matter of the environment from indiscriminately entering the living system. The current concept of the skin barrier suggests that permeability is governed by a hydrophilic and a hydrophobic "channel". To account both for the barrier function and the hydrophilic and hydrophobic pathways through this barrier, we propose a new model, "the domain mosaic model of the skin barrier", which depicts the bulk of the lipids as segregated into crystalline/gel domains bordered by "grain borders" where lipids are in the fluid crystalline state. Such an arrangement provides for an effective "water-tight" barrier that allows a minute and controlled loss of water to keep the corneocytes moistened. In addition the model provides for the necessary mechanical properties permitting bending and stress imposed on the skin surface. Furthermore, the fluid character of the "grain borders" represents areas where lipid and hydrophobic molecules may diffuse through the system on down-hill gradients. It is suggested that in the border areas between the crystalline domains, structural transformations of the lipid organization due to permeation promoters may take place without structural changes in the bulk organization of lipids in the crystalline or gel phase.