Retinoic acid(Tretinoin) is commonly used in dermatology drugs, which is the department of vitamin A (Victoria methanol) metabolic intermediates.It mainly affects the growth of bones and epithelial metabolism, can promote epithelial cell proliferation and updates, and can inhibit the proliferation and differentiation of keratinocytes, so hyperkeratosis can be back to normal. Therefore many complete or incomplete keratosis, hyperkeratosis of diseases have a certain therapeutic effect, treat a variety of skin diseases. The use of the drug can penetrate topical skin quickly, enable significantly increased epithelial cell turnover. This class of drugs has strong and rapid inhibition on the secretion of the sebaceous glands, can reduce sebum secretion. In addition, the product also has anti-tumor, promote wound healing and anti-inflammatory effects.