The causes of fever can be categorized into infectious fever, malignant neoplastic disease fever, immune system disease fever and drug fever. 1. Infectious fever: When the body is infected with microorganisms such as bacteria, virus or chlamydia, fever may occur. 2. Fever of malignant tumor disease: When you suffer from various malignant tumor diseases such as lung cancer, leukemia or pancreatic cancer, you will have fever for a long time. 3. Fever from immune system diseases: immune system diseases such as systemic lupus erythematosus and polyarteritis nodosa will affect the immune system and cause fever. 4. Drug fever: Fever caused by the use of certain drugs is non-infectious fever. The cause of fever is more complicated, patients should go to the hospital in time to clarify the cause of the disease, choose the appropriate method to treat the disease.