Premature skin aging caused by repeated exposure to solar radiation is called 
photoaging. Although once considered an irreversible process, it is now 
established that photoaging can be treated by topical tretinoin. Both from 
carefully designed controlled clinical studies; and basic investigations into 
the mechanism by which tretinoin improves photoaged skin, our understanding of 
photoaging has been enhanced. This article highlights some of these studies 
which have contributed to our knowledge.