Aging and photoaging of the skin

Abstract

Key Features: Skin is the largest organ of the human body. Skin is the first barrier against infection, and protects the internal organs from temperature and water loss, and from physical injuries. Skin also transmits sensory information (pressure, temperature, pain), and skin appendages produce hair, sweat, and oils (sebum). The integrity of the skin is vital for the human body. Aging is accompanied by a decline in the appearance and function of the skin. Clinically, a clear distinction is made between natural (or intrinsic) aging, and extrinsic or photoaging (premature aging due to chronic exposure to ultraviolet [UV] irradiation). However, these two entities share common biochemical mechanisms that lead to altered skin structure and function. Both natural and photoaging are characterized by decreased quality and quantity of type I collagen, the major structural protein of the skin connective tissue (dermis) Oxidative stress, which increases over time or after each UV exposure, activates various cellular signaling pathways that stimulate production of collagen-degrading enzymes. Chronic oxidative stress results in fragmentation of dermal collagen fibers and loss of the mechanical tension that normally maintains the dermal structure. Dermal cells respond to low mechanical tension by reducing their collagen production and by increasing collagen fiber breakdown. Thus, the deterioration of skin structure that accompanies skin aging is a self-sustained mechanism. Interventions that aim to increase collagen production by dermal cells (fibroblasts) and/or restore mechanical tension in the dermis provide varying degrees of efficacy for treatment of the clinical signs of skin aging. © 2010 Springer-Verlag Berlin Heidelberg.