Tretinoin's effectiveness as an acne medication is because of its ability to modify the abnormal follicular formation that comes from excessive keratinization of epithelial cells. Tretinoin promotes cornified cell detachment and enhances shedding. Tretinoin increases mitotic activity, thereby increasing loosely-adherent corneocytes turnover. By doing so, the comedo contents can be expelled, with a reduction of microcomedo precursor lesion of acne vulgaris