Psoriasis has always been a difficult disease to treat, but the emergence of retinoic acid has brought a boon to the treatment of psoriasis, and it is by far the most effective drug for the treatment of psoriasis. Mechanism of action: Retinoic acid, also known as retinoic acid, is a metabolic intermediate product of vitamin A in human body, which promotes the occurrence of normal keratinization and affects epithelial metabolism by regulating the mitosis of epidermal cells and the renewal of epidermal cells, and has an obvious role in promoting the growth of epithelial keratinocytes and the shedding of keratin layer; it can prevent the blockage of keratin plugs and has an inhibitory effect on the synthesis of keratin. Retinoic acid is divided into three generations according to its structure. Indications: Treatment of psoriasis, acne, ichthyosis, hair erythroderma, follicular keratosis and other keratotic diseases. Usage: Adults: Depending on body weight, the starting dose is 25-50mg/day, preferably taken with meals or milk to ensure better absorption of the drug, generally treated for 1-2 months and gradually reduced after symptoms improve. Children: In view of the serious side effects that may result from long-term treatment, the pros and cons should be carefully weighed. Avelox should only be considered if all available treatment options have proven ineffective. It is contraindicated in persons planning a recent pregnancy and in pregnant women. Side effects: 1. Dry skin and dry mouth may occur, due to the inhibition of sebum secretion by the drug. The drug will be tolerated after a few days, but if it is not tolerated, it should be discontinued. 2, affect the liver function, blood lipids, need regular review, if the index is too high need to stop the drug. 3. Teratogenic effect, excessive ossification, extra skeletal calcification, bone thinning, osteoporosis, early closure of epiphysis. Those who plan to get pregnant and pregnant women should not take it for 2 years. 4, try to avoid sun exposure after application to avoid the formation of irritant dermatitis.