Epidermal barrier represents one of the essential conditions of life on Earth. However, our present understanding of its function is still insufficient. The role of water incorporated in stratum corneum has not been yet studied enough. Till recently, both the stratum corneum et granulosum were considered to be „dead“ layers. It turned out that these layers form very active part of epidermis and they have a secretory function. Their rigid anhydrotic consistency, complex intercellular spaces, and lipid bilayers produced by lamellar bodies form the defense barrier against both the loss of fluids and ions and protecting against the hostile external environment. Important stabilizing function in the barrier has ceramides and urea. The Langerhans’ dendritic cells and macrophages induce production of cytokines in keratinocytes by means of calcium signals. That triggers the inflammatory cascade, which is accompanied by formation of pathological types of T-cells and by activation of apoptosis. Last but not least, the impairment of epidermal barrier has an important role in the physiological aging of the skin.

        Key words: epidermal barrier, lipid bilayers, ceramides, dendritic cells, lamellar bodies, urea, atopy.