Horny layer molecular structure: A new theory for hydrophilic molecules free diffusion through the skin

Author shows a novel molecular theory capable to describe the passage of hydrophilic molecules and solutes through the horny layer (HL). According to the theory of the "gear wheels" the hydrophilic groups of the intercorneal lipids and especially ceramydes and free fatty acids, components of the lipidic domains, are oriented toward the hydrophilic head of the horny cells, represented by the aminoacidic appendages and humectants substances derived from the epidermal cells proteins catabolism (NMF). This mutual orientation would create aqueous zone placed between the surface of lipids domains surface and the surface of corneocytes so creating aqueous channels in which hydrophilic molecules can be solved in andflow toward the deepest skin layer moved by a mechanism similar to a "gear wheel" device. The molecules and solutes, so, could move for free diffusion or attracted by the aqueous gradient taking place through the adjacent different water content zones. This molecular theory could explain the penetration of high molecular weight hydrophilic molecules such as hyaluronic acid (HA) through the skin, thanks to the capability to hydrate in the water fulfilled channels placed in the space between lipids bi-lamellar domains and horny cells surface. It has been demonstrated that HA can penetrate deeply and quickly through the skin reaching dermal layer. Previous scientfic investigations on the HL structure clarified that skin surface exposure to a prolonged contact with moisture or water solutions produces a dramatic alteration of the HL inducing formation of "aqueous cisternae" and a geometric-structural alteration of the bi-layers inter-corneal lipids. This evidence supports the hypothesis according to which water can penetrate through the shin by mean of hydrophilic paths and then "enlarge" horny cells. Furthermore, this theory would open the path of investigation of new promising and performing new class of skin absorption enhancers even for hydrophilic drugs and cosmetics.