Avia is a second generation retinoic acid drug, which is the metabolite of Avia ester in the body, with stronger biological activity and similar efficacy to Avia ester, with a half-life of 2-3 days. It has the effect of regulating epidermal cell differentiation and proliferation, and is mainly used for the treatment of severe psoriasis, such as erythrodermic psoriasis and pustular psoriasis, and also for the treatment of dyskeratotic skin diseases, such as congenital erythrodermic ichthyosis, hair erysipelas, and follicular keratosis. The main adverse effects include dryness of the skin mucosa and photosensitivity, headache, tinnitus, early closure of the bones, musculoskeletal pain, abnormal liver function and elevated blood lipids, it also has teratogenic effects and women of childbearing age must use effective methods of contraception for at least two years after stopping treatment.