The causes of persistent low fever are more, mainly as follows: 1, infection: infection is a common cause of persistent low fever, such as after infection with tuberculosis, active tuberculosis patients can be manifested as persistent low fever. Tuberculosis caused by low fever, to the afternoon, evening mainly, clinically generally known as afternoon fever. In addition to tuberculosis, other pathogens can also cause low-grade fever, such as respiratory viral infections, urinary tract bacterial infections can also cause low-grade fever; 2, non-infectious diseases: such as rheumatism, malignant tumors, in particular, some of the drugs can also cause fever. No matter which cause, if the patient has a low fever in a short period of time, it can be observed without excessive anxiety, and if the fever can be relieved by itself within 3-5 days, no further special treatment is needed. If the fever persists for more than 1 week, or if the patient still has other discomforts, such as headache, diarrhea, or cough, then the patient needs to consult a doctor as soon as possible to find out the root cause, without the need to use drugs to reduce the fever.