Tretinoin (topical vitamin A acid) has unique mechanisms of action compared to other anti-acne agents. Tretinoin increases follicle wall cell turnover and decreases cohesiveness of cells; as a result, existing comedones are extruded and the formation of new comedones is inhibited. Thus, this drug is very effective in removing blackheads. Tretinoin also decreases the number of cell layers in the stratum corneum. Tretinoin, like benzoyl peroxide, can be very irritating, especially to fair skin, and the guidelines to decrease the potential for irritation for both of these drugs are the same. Tretinoin also increases the susceptibility to irritation from wind, cold, dryness, and sunlight, all of which should be avoided as much as possible.