Afternoon fever is caused by several factors: First, infectious fever, the most common fever caused by tuberculosis infection, with pulmonary tuberculosis and intestinal tuberculosis as common symptoms, such as viral infection causing high fever, the upper respiratory tract viral infection, pulmonary viral infection as typical clinical symptoms, will occur in the afternoon high fever. Rare pathogens such as atypical pathogens, mycoplasma, and chlamydia infections also present with symptoms of high fever starting in the late afternoon. Second, non-infectious inflammatory diseases resulting in high fever, when clinical symptoms such as hematologic diseases, tuberculosis, immunologic diseases, rheumatic diseases, and connective tissue diseases, also occur in the afternoon. Third, endocrine metabolic diseases, such as hyperthyroidism and hyperadrenocorticism, can also present with a neurological upward shift of the body temperature regulating point, which can cause high fever in the afternoon due to high catabolic state.