There are many causes of erythema multiforme, which may be caused by microbial infection factors, as well as drugs, systemic diseases, environment and other factors. 1. Microbial infection: erythema multiforme may be caused by bacterial, viral, fungal, mycoplasma and other pathogenic microbial infections, and it is recommended to consult the dermatology department for treatment under the guidance of doctors. Daily to do a good job of skin protection, avoid injury. 2. Drug factors: If you use antibiotic drugs, antipyretic and analgesic drugs, anti-tuberculosis drugs, etc. for a long time, which cause allergic reaction and immune reaction, it will lead to the occurrence of erythema multiforme. It is recommended to stop the medicine in time and consult the doctor immediately. 3. Systemic diseases: If you suffer from systemic lupus erythematosus, malignant tumor, tuberculosis, rheumatic fever and other systemic diseases, it will also cause erythema multiforme. 4. Environmental factors: polymorphic erythema can be caused by contact with certain allergens in daily life, such as metal agents, chemical agents, or sun exposure, trauma, cold and other factors, so avoid contact with allergens in daily life. Avoid contact with allergens in daily life. Maintain good hygiene habits and clean the skin in time. It is suggested that patients with erythema multiforme should consult the doctor in time, so as to clarify the cause of the disease as soon as possible and treat it in time.