Tretinoin was shown in the late 1960s to be useful for the treatment of 
disorders associated with abnormal epithelial differentiation; however, because 
of irritation, retinoids were only slowly accepted. In the 1970s, evidence 
accumulated to show that topical tretinoin could modulate many of the 
abnormalities in the epidermis and dermis associated with photoageing. It has 
been shown in hairless mice that tretinoin can reverse dermal elastosis with the 
formation of new collagen and this has led to clinical trials being carried out 
in man. Randomized, controlled trials have shown that topical tretinoin is 
effective in the treatment of photoaged skin.