Unexplained nighttime fevers in the elderly may be caused by infections, autonomic dysfunction, tumors, and other diseases. 1. Infection: the body reserve function of the elderly decreases and the susceptibility to infection increases, which may be caused by viral infection, tuberculosis mycobacteria infection, bacterial infection and other fevers. 2. Autonomic dysfunction: autonomic dysfunction of the elderly will affect the normal thermoregulation process, and the body’s heat production is greater than heat dissipation, which will cause the body temperature to rise, and the symptom of unexplained fever at night may occur. 3. Tumor: the old man suffers from tumor diseases, such as leukemia, Hodgkin’s lymphoma, etc., which will lead to tissue cell necrosis, the release of tumor necrosis factor and other pyrogenic cytokines and the absorption of aseptic necrotic products, which will make the body feverish, and there are also the symptoms of unexplained fever. The causes of unexplained fever in the elderly are more, the condition persists or accompanied by physical discomfort it is recommended to go to the hospital in time for examination and treatment.