Tretinoin, also referred to as all-trans retinoic acid, is used to treat acne. It can be purchased as a cream, gel, or ointment. It functions by accelerating cell division to replace dead cells with new ones more quickly and avoid blocking skin pores. Dark spots, fine lines, and wrinkles can also be effectively treated with tretinoin cream. When the skin being treated is shielded from the sun, it functions best.