Recurrent high fevers in the elderly can be caused by infections, tumors, immune system disorders, etc. It can also be seen in blood diseases, etc. 1. Infection: if bacterial infection, such as legionella, parasites, new viruses, etc., due to rare pathogens in the early stage of the disease is difficult to isolate, the treatment is not timely, which leads to the occurrence of unremitting fever. 2. Tumor: malignant tumors often have recurrent fever in the late stage, such as tumors occurring in the lung parenchyma and mesenchyme, hemoptysis, wheezing, chest tightness, chest pain, fever, fatigue and other symptoms, the elderly body resistance is poor, low immunity, there will be a high fever recurrent phenomenon. 3. Immune system diseases: low immunity and immune disorders in the elderly lead to abnormal TB lymphocytes, which release various inflammatory factors, such as interleukin 1, interleukin 6 and anti-tumor necrosis factor. Under the stimulation of inflammatory factors, it will affect the regulation point of the thermoregulatory center of the brain, so that the regulation point rises, thus appearing the phenomenon of high fever that does not go down and back and forth. If the old man has a high fever that does not go away, it is recommended to go to the hospital as soon as possible for examination, according to the specific situation, follow the doctor’s advice, and actively cooperate with the treatment.