Mechanisms and Pathophysiology of Photoaging and Chronological Skin Aging

Research conducted during the past 25 years has produced an understanding of the mechanisms that lead to connective tissue damage during chronological aging and as a result of chronic, repetitive exposure to ultraviolet (UV) radiation from the sun. While the etiologies of these two conditions are distinct, they share common pathophysiological mechanisms. In both conditions, upregulation of collagen-degrading matrix metalloproteinases (MMPs) and fragmentation of the major connective tissue elements of the dermis (primarily type I collagen) occurs. For a while, new collagen production keeps up with collagen damage, but eventually the amount of damaged collagen in the skin increases. At that point, the signs of aging and photoaging become evident.