Erythema multiforme is related to infection factors, drug factors, disease factors, physical factors and other causes. 1. Infection factor: Herpes simplex virus is the most common causative factor of erythema multiforme, if patients are infected with herpes simplex virus, it may induce the disease. 2. Drug factors: if there is abnormal metabolism of drugs after taking antibiotics such as penicillin, amoxicillin or anticonvulsants such as carbamazepine and phenytoin sodium, erythema multiforme may also be induced. 3. Disease factors: if suffering from systemic lupus erythematosus, tuberculosis, multiple myeloma, rheumatic fever and other diseases, erythema multiforme can also be induced. 4. Physical factors: the disease may also be induced by cold environment, long-term exposure to sunlight or trauma. For patients with erythema multiforme, it is recommended to go to regular hospitals for consultation and examination to clarify the cause of the disease.