There are many diseases that cause fever, which can be classified as infectious diseases according to their etiology, including infectious diseases commonly caused by various pathogens, such as bacteria, viruses, fungi, and mycoplasma. Infectious fever caused by bacteria is the most common, followed by viruses. There are also: 1) non-infectious diseases, such as hematological diseases and malignancies, such as leukemia, malignant histiocytoma, malignant lymphoma, colon cancer, and primary liver cancer; 2) allergic diseases, such as drug fever and rheumatic fever; 3) connective tissue diseases, such as systemic lupus erythematosus, dermatomyositis, polyarteritis nodosa, mixed connective tissue diseases, and others, such as hyperthyroidism, hyperthyroid crisis, severe water loss or bleeding pyrexia, heat stroke, fracture, massive burns, cerebral hemorrhage, craniocerebral trauma, persistent epilepsy, heart failure, visceral vascular infarction and infarction, and tissue necrosis.