The efficacy of tretinoin is well established in the treatment of acne and 
photoaged skin, however as a typical side effect of tretinoin treatment most 
patients develop a low-grade irritant dermatitis. Since isotretinoin topical 
treatment usually shows much lower incidence and intensity of adverse effects 
than tretinoin topical treatment, histological studies are needed to 
scientifically evaluate the effects of isotretinoin application on epidermis and 
also to assess if it can be used in anti-aging products as an alternative to 
tretinoin. Thus, the aim of this study was to compare the effects of topical use 
of tretinoin or isotretinoin on hairless mice epidermis, using appropriate 
histopathological and histometric techniques, in order to evaluate the influence 
of isomerism on skin effects. For this, gel cream formulations containing or not 
0.05% tretinoin or 0.05% isotretinoin were applied in the dorsum of hairless 
mice, once a day for seven days. Histopathological evaluation, viable epidermal 
and horny layer thicknesses as well as the number of epidermal cell layers were 
determined. Our results showed that tretinoin and isotretinoin were effective in 
the enhancement of viable epidermis thickness and number of epidermal cell 
layers, suggesting that they could be used for stimulation of cellular renewal. 
However isomerism influenced skin effects since isotretinoin had more pronounced 
effects than tretinoin in viable epidermis. In addition only isotretinoin 
treatment enhanced horny layer thickness when compared to the gel cream 
treatment.