Premature skin aging, or photoaging, results largely from repeated exposure to 
ultraviolet (UV) radiation from the sun. Photoaging is characterized clinically 
by wrinkles, mottled pigmentation, rough skin, and loss of skin tone; the major 
histologic alterations lie in dermal connective tissue. In recent years, a great 
deal of research has been done to explain the mechanism by which UV induces 
dermal damage. This research has enabled the identification of rational targets 
for photoaging prevention strategies. Moreover, studies that have elucidated 
photoaging pathophysiology have produced significant evidence that topical 
tretinoin (all-trans retinoic acid), the only agent approved so far for the 
treatment of photoaging, also works to prevent it. This article summarizes 
evidence mainly from studies of human volunteers that provide the basis for the 
current model of photoaging and the effects of tretinoin.