Topical retinoids are been used to successfully treat acne for almost 3 decades. At the beginning, a retinoid was a compound of similar structure and action to retinol (vitamin A).(1) Changes at the carboxylic end group, the polyene chain, and the aromatic ring can result in the modification of the original molecule. To date, three generations of retinoids have been developed: the nonaromatics (retinol, tretinoin, and isotretinoin), the monoaromatics (etretinate and acitretin), and the polyaromatics (arotinoid, adapalene, and tazarotene). The new synthetic retinoid molecules have little resemblance with retinol but nonetheless are included in this family because they have the ability to bind with or activate retinoid receptors. Therefore, retinoids are vitamins and also hormones.(3)