Tretinoin is a topical liquid, cream or gel most commonly used for the treatment of acne. Tretinoin is said to control acne, but is not a cure for it. It initially works topically and, with continued use, penetrates the top layer of the skin to reduce the formation of acne and help acne heal more quickly over time. Users of tretinoin may experience a decrease in the number of acne pimples, as well as the severity. Tretinoin promotes the peeling of skin affected by acne and unclogs pores to nurture healthier skin. Tretinoin requires a prescription and may be prescribed for other uses, such as in the treatment of leukemia, where tretinoin, in the form of a pill, promotes the development of healthy, functional cells.