Dry skin is the most common clinical manifestation of dermatologic diseases, and it presents with itching, redness, and desquamation—signs and clinical manifestations that are not only physically uncomfortable but also affect patients psychologically.  The water content in the stratum corneum is largely dependent on the composition and amount of the intercellular lipids, which regulate the loss of water from the skin, and on the levels of hygroscopic substances of the natural moisturizing factors, which are responsible for retention of water in the stratum corneum.  Prevention of water loss and penetration of potentially toxic substances and microorganisms into the body are the most important functions of the skin, which acts as a natural frontier between the inner organism and the environment.  Skin barrier defects occur in several skin diseases, but the influence of aging on the skin barrier function is largely unknown and conflicting results have been reported.  In this review, the structure and function of the barrier in relation to the aging process are discussed.