The cause of rheumatoid arthritis is not completely clear, rheumatoid arthritis is a disease closely related to the environment, cells, viruses, genetics, sex hormones and neuropsychiatric state and other factors. 1, bacterial factors Experimental studies have shown that group A streptococci and peptidoglycan (peptidoglycan) may be a continuous stimulus for the development of RA, group A streptococci long-term presence in the body to become a continuous antigen, stimulating the body to produce antibodies, immunopathological damage and disease, mycoplasma created by the animal model of arthritis and human RA is similar, but does not produce human RA is unique The rheumatoid factor (RF) of human RA. Bacterial or bacteriophage antigenic substances have never been found in the joint fluid and synovial tissue of RA patients, suggesting that bacteria may be related to the onset of RA, but direct evidence is lacking. 2, viral factors The relationship between RA and viruses, especially EBV, is one of the issues that scholars at home and abroad have paid attention to. Studies have shown that arthritis due to EBV infection is different from RA, and RA patients have a stronger reactivity to EBV than normal people, and a persistent high level of anti-EBV-cytoplasmic antigen antibodies appear in the serum and synovial fluid of RA patients, but so far However, to date, no antibodies to EBV nuclear antigen or shell antigen have been found in the serum of RA patients. 3, genetic factors The disease has a high incidence in some families, in a population survey, found that human leukocyte antigen (HLA)-DR4 is associated with RF-positive patients, HLA studies have found that DW4 is associated with the onset of RA, 70% of patients are HLA-DW4 positive, patients have a susceptibility gene for this point, so genetics may play an important role in the development. 4, sex hormones Studies have shown that the ratio of male to female incidence of RA is 1:2 to 4. The disease is reduced during pregnancy, and the incidence is reduced in women taking birth control pills. Animal models show that LEW/n female rats have a high susceptibility to arthritis, while males have a low incidence, and after male rats are castrated or treated with β-estradiol, their incidence of arthritis is the same as that of female rats, indicating that sex hormones play a role in the development of RA. Cold, humidity, fatigue, malnutrition, trauma, and psychological factors are often predisposing factors for the disease, but most patients often have no obvious predisposing factors to be identified before.