Skin Barrier Function

Abstract

Skin acts as a biological barrier protecting the body from external insults; externally protecting it from pathogens, chemicals, UV radiation, and allergens; internally helping to maintain the homeostasis and protect the body from enhanced loss of water, electrolytes and proteins. The permeability barrier function is situated in the epidermis and primarily in the stratum corneum (SC) that, representing the outermost 10-20 μm of the epidermis, is made up of corneocytes, flattened dead squamous cells, filled with keratinocyte filaments enclosed by an envelops of cross-linked proteins, and surrounded by a semi-continuous, highly organized, lipid lamellae matrix. These filaments are aggregated by filaggrin (FLG) protein which, next together with several other proteins, is cross-linked into a mechanically robust cornified cell envelop. This envelop, that provides a scaffold for the extracellular lipid matrix, is an important component for the SC structural and mechanical integrity. Moreover, the products of FLG degradation account in part for the water-holding capacity and maintenance of acidic pH of the SC, necessary to regulate the activity of different enzymes which control desquamation, lipid synthesis, inflammation, and, therefore, the epidermal barrier homeostasis.