The etiology of low fever in the afternoon is often complex. First, it is important to exclude afternoon fever caused by Mycobacterium tuberculosis infection. In the case of Mycobacterium tuberculosis infection, afternoon hot flashes are likely to occur, often accompanied by generalized wasting and night sweats. In the case of pulmonary tuberculosis, there is also a pronounced cough, sputum, and sometimes hemoptysis, so it is necessary to go to the hospital for chest X-ray, blood tests, and tuberculin tests. Secondly, rheumatic immune system diseases may also lead to long-term low fever symptoms, and often also afternoon low fever, so it is necessary to do rheumatic immune system examination. Finally, it is not excluded that malignant tumors cause afternoon low fever symptoms, which are also relatively common, especially blood system tumors or other parts of the tumor, may lead to afternoon low fever symptoms, so it is necessary to do specific physical examination.