The cause of psoriasis is complex and still unknown. In recent years, most scholars believe that it may be related to genetics, infection, metabolic disorders, immune dysfunction and endocrine disorders. Although psoriasis experts all over the world have been studying it for many years, it still cannot be cured at present. According to preliminary clinical observation, the onset of psoriasis is related to the following factors: i. Genetic factors. It is mostly believed that the disease is controlled by multiple genes and also influenced by other external factors. Second, infection factors. Some people believe that it is due to viral infection, although eosinophilic inclusion bodies have been found in the nucleus of epidermal spiny cells, but so far the virus culture has not been successful. Streptococcal infection may be an important precipitating factor for this disease, because acute punctate psoriasis often has acute tonsillitis or upper respiratory tract infection before the rash. Third, metabolic disorders. There are reports of increased serum lipids, cholesterol, globulin, sugar, uric acid, potassium, etc., and decreased folic acid content, but no definite conclusion can be made. Increased polyamines and arachidonic acid in the skin lesions have also been reported. Fourth, immune dysfunction. Some patients have low cellular immune function; some have increased serum IgG, IgA, IgE; some patients have anti-IgG antibodies in the serum; some have measured anti-keratin autoantibodies in the epidermal stratum corneum with immunofluorescence technology. V. Mental factors. Mental trauma and emotional stress and overexertion can trigger the disease or aggravate the disease. Sixth, other factors. Most patients relapse and aggravate in winter, remission or natural remission in summer, but the seasonal regularity disappears in patients with long-standing disease. Some women also suffer from aggravation before and after menstruation, and the rash subsides during pregnancy and relapses after delivery. Chloroquine, lithium carbonate and β-adrenergic blocking drugs can aggravate the disease. It is generally believed that the cause of psoriasis must have two factors, one is the existence of the patient’s own susceptibility gene for psoriasis. The second is the encounter with adverse related external stimuli.