Fever up to 38 ℃, suggesting low fever. 90-year-old people with low fever, may be related to viral infections, bacterial infections, tuberculosis, hyperthyroidism, tumors, and cerebrovascular lesions and other factors, need to be based on different causes, to take targeted treatment, and there is no such thing as the best way to solve the problem. 1. Viral infection can cause fever, due to the self-limiting nature of the disease, in the case of a good mental state, the main thing is to pay attention to drink more water, pay attention to more rest, you can also use the way of wiping to reduce the body temperature. Antiviral drugs are given when necessary. 2. Bacterial infection caused by low fever, you need to choose some sensitive antibiotic treatment, such as cefuroxime, amoxicillin clavulanate potassium and so on. 3. Low fever caused by tuberculosis needs to be treated with anti-tuberculosis drugs, such as rifampicin capsules, isoniazid tablets, ethambutol and so on. 4. Hypothermia caused by hyperthyroidism, need to give anti-thyroid treatment, such as methimazole tablets. 5. Low fever caused by tumor, anti-tumor treatment is needed, such as oral capecitabine, tiglio capsule to treat digestive tract tumors, but also according to the physical conditions, the type of disease, surgical treatment, radiotherapy and so on. 6. Hypothermia caused by cerebrovascular lesions is mainly related to the damage of thermoregulatory center, generally preferred to physical hypothermia, and at the same time, need to be treated according to the cause of the disease, for example, give mannitol injection to dehydration and lower intracranial pressure treatment. Due to the complexity of the etiology, the doctor should analyze and choose the treatment plan in combination with other clinical manifestations.