What is the mechanism of action of oral isotretinoin in acne vulgaris?

Like tretinoin, the mechanism of action has not been precisely determined. Isotretinoin is the most effective known inhibitor of sebum production (up to 90% inhibition). Because clinical improvement in acne vulgaris appears to correlate with a reduction of sebum production, this is believed to be the most important mechanism of action. Isotretinoin also markedly affects keratinization and probably exerts an effect on the cohesiveness of the follicular keratinocytes, thus reducing microcomedone formation. Less important actions include antiinflammatory effects, antibacterial effects, and inhibition of microbial enzyme activity.