Epidermal barrier function and systemic diseases.

The skin is a vital organ for life and, among its many functions, the role as a protective barrier is one of the most important. It is the main boundary between the body and the external environment. As defensive barrier, the epidermis protects internal organs from physical and chemical trauma, microorganism invasion, and ultraviolet radiation. It also acts in the regulation of transepidermal movement of water and electrolytes, and in preventing dehydration, all of which are essential for sustaining life. The main role is allotted to the stratum corneum and to the lipid matrix located in the intercellular space. The occurrence of dysfunction in the epidermal barrier is an important factor in the physiopathogenesis of skin diseases, particularly atopic dermatitis and psoriasis. There are few, but important, systemic changes that influence or are influenced by dysfunctions in the epidermal barrier. We review the effects of some systemic diseases on the maintenance of the skin's homeostasis.