What is the mechanism of action of tretinoin in acne vulgaris?

The precise mechanism of action is not proved, but tretinoin is believed to exert its therapeutic effect by decreasing the cohesiveness of follicular epithelial cells that are responsible for producing microcomedones. Microcomedones are the earliest recognizable abnormality in acne vulgaris. Tretinoin also stimulates mitotic activity of follicular keratinocytes, promotes extrusion of comedones by rapid cell turnover, and decreases the production of sebum, although this effect is minimal.

Bikowski JB: Mechanisms of the comedolytic and anti-inflammatory properties of topical retinoids, J Drugs Dermatol 4:41–47, 2005.