Low fever at night in the elderly may be caused by tuberculosis, chronic biliary tract infection, chronic urinary tract infection, endocrine disease, rheumatic immune disease, tumor and so on. 1. Tuberculosis is the most common cause of low fever, often with low fever, night sweats, fatigue, emaciation and other symptoms. 2. Chronic biliary tract infections: such as chronic cholecystitis, chronic cholangitis, etc. Inflammatory stimulation leads to nighttime low-grade fever in elderly patients, which may be accompanied by decreased appetite, nausea, vomiting and other symptoms. 3. Chronic urinary tract infections: such as chronic pyelonephritis, chronic prostatitis, etc. Inflammatory stimulation can cause low-grade fever, accompanied by frequent urination, urinary urgency, dysuria and other symptoms. 4. Endocrine diseases: such as hyperthyroidism, diabetes mellitus and other endocrine disorders, causing low fever symptoms. 5. Rheumatic immune system diseases: such as systemic lupus erythematosus, patients with multiple organ and system involvement, can also cause temperature changes, low fever at night. 6. Tumor: malignant tumors cause dysregulation of the body temperature regulating center and make patients suffer from nighttime hypothermia. In addition, there are some non-pathological factors, such as mood swings, tension and anxiety, which can also lead to a mild increase in body temperature and symptoms of low fever. There are more reasons for low fever in the elderly, so you can consult a doctor in time, provide a detailed medical history, and carry out examination and treatment under the guidance of the doctor, so as to avoid delaying the condition.