The causes and pathogenesis of psoriasis are not yet completely clear, and it is now internationally and domestically recognized that it is the result of the joint action of genetic and environmental factors, that is, it is induced by a variety of factors on the basis of genetic factors, and the report of the national epidemiological survey of psoriasis in 1984 showed that 32% of people have a family history of heredity, and the mode of inheritance is autosomal dominant, and the epistatic rate accounts for 20%. Common predisposing factors are as follows: 1. Infection is one of the important predisposing causes of psoriasis, especially in pediatric patients. It is reported that psoriasis patients with chronic tonsillitis account for more than 90%, following acute inflammation of the tonsils psoriasis patients account for 49.5%, children with psoriasis often accompanied by upper respiratory tract infection and tonsillitis, psoriasis patients with streptococcal infection can often deteriorate rapidly, the application of antibiotic treatment can often reduce psoriasis, it can be seen that upper respiratory tract infection and tonsillitis and psoriasis have a certain The relationship between upper respiratory tract infection and tonsillitis and psoriasis may be the organism’s metamorphic reaction to the toxin of bacteria. 2, immune dysfunction Immunological studies have confirmed that the humoral immunity of psoriasis patients is disturbed, T suppressor cells in the blood of patients are significantly decreased, T helper cells are elevated, cellular immune function is low, lymphocyte transformation rate and natural petal formation rate are reduced, and skin delayed hypersensitivity reaction test is weakened, and it is also reported that the infiltrating cells at the site of psoriasis lesions are mainly T cells, and these cells have surface HLA-DR and LL-2 receptor expression, can secrete some cytokines, by the role of these factors, can trigger a series of metabolic abnormalities of keratinocytes in the lesion area, causing psoriasis lesions. The important pathophysiological change of psoriasis is the acceleration of epidermal cell proliferation, which shortens the epidermal cell turnover time. The normal epidermal cell turnover time is 26-28 days, while the turnover time of psoriatic lesions is 3-4 days, thus the maturation of epidermal cells is disturbed, resulting in disorders of epidermal histology, serialization and keratinization, producing a series of pathological phenomena such as silvery white scales. Such rapid growth of epidermal cells in psoriasis may be directly related to the action of a substance called “polyamine”, which is an important regulatory substance in cell biology, especially related to the biometabolism of DNA and RNA proteins. Proteins combined together, through accelerated enzyme reactions and direct action, causing accelerated cell division and shortened cell turnover time, resulting in some pathological changes of psoriasis. 4, endocrine dysfunction Clinical data show that female patients are related to menstruation and pregnancy, and most patients improve during menstruation and pregnancy, and the improvement of skin lesions mostly occurs within 3-6 months after pregnancy, while most patients’ condition is aggravated after delivery, which may be related to the increased secretion of corticosteroids during pregnancy. 5, mental factors People have long recognized that the skin is one of the organs of expression of human internal mental activities, excessive mental tension is a non-negligible trigger for the onset and deterioration of psoriasis, due to excessive mental tension, anxious temperament, emotional depression, irritability and insomnia and other mental factors do triggers, accounting for the first of all other triggers, data show that about 18.6%. Excessive mental tension produces a series of psychological or physiological reactions, promotes endocrine disorders, damages the immune defense system of the body as well as the metabolic disorders of enzymes, thus promoting the occurrence of psoriasis. This situation is often encountered in clinical practice, psoriasis patients have been cured for many years without relapse, due to great mental stimulation, such as the death of relatives, fights and brawls, etc., so that patients are overly nervous, followed by insomnia and dreaminess, distracted, and then feel hot, itchy, psoriasis lesions, this situation is common in clinical work. 6, trauma The phenomenon that psoriasis lesions occur after trauma is very common, such as bruises, injections, insect bites, burns and scratches, etc. These stimuli can cause skin damage, and then induce the occurrence of psoriasis. 7, other such as allergies, cold, humidity, dry climate and high temperature are also common triggering causes of psoriasis.