Retinoic acid (tretinoin), like  benzoyl peroxide,  has been available for at least twenty years, initially as an ointment which was unsuitable for patients with acne but, in the  last fifteen years,  as highly acceptable cosmetic preparations, in particular as a gel and a cream (usually in a concentration of 0.025 per cent to 0.05 per cent). The drug is  especially helpful in reducing the number of noninflamed lesions,  which has  been  demonstrated in clinical studies and by using the follicular cast technique  as a measure of the number of microcomedones.

Since noninflamed lesions are responsible for the subsequent development of some inflamed lesions, retinoic acid indirectly  suppresses the number of inflamed lesions. The mechanism of the  drug  has been  studied predominantly in  terms of its role in influencing comedogenesis.

 

   Secondary to its effect on comedogenesis, retinoic acid possibly  reduces  ductal  P.  acnes,  presumably because it renders  the duct environment alien to the growth of P. acnes.

 

   Limited studies  in  this author's department have shown no effect of retinoic acid on sebum  excretion rate.