The causes of fever and coldness in 90-year-olds include infectious diseases, autonomic dysfunction, and psychiatric diseases. 1. Infectious diseases: when there are viral infections, bacterial infections, Mycobacterium tuberculosis and other infections in the elderly, the body temperature rises, and the patient will have a feeling of hot and cold. For viral infections, antiviral drugs such as ganciclovir and acyclovir should be used as prescribed by the doctor. Bacterial infections should be treated with sensitive antibiotics, such as melocillin sodium and ceftriaxone. Mycobacterium tuberculosis infection should be treated with active anti-tuberculosis therapy, e.g. isoniazid, rifampicin, streptomycin. 2. Autonomic dysfunction: 90-year-olds with irregular daily life and excessive psychological pressure can lead to autonomic dysfunction. Patients may have cold and hot feeling, accompanied by dizziness, headache, chest tightness, palpitation and other symptoms. Oral medication such as glutamine and vitamin B12 can be prescribed to regulate the nerves. Psychological stress can be excessive to the psychological clinic, behavioral cognitive therapy. 3. Mental illness: At the onset of this disease, the patient will have self-conscious symptoms, such as cold and hot. According to the patient’s condition, the use of antipsychotic drugs, such as olanzapine, iproniazine, etc., in accordance with medical advice. The above are only some of the common causes. 90 year olds with symptoms of hot and cold spells should go to the internal medicine clinic as soon as possible to have the cause of the disease identified and treated. The use of the above drugs must follow the doctor’s instructions, not blindly use their own drugs, in order to avoid adverse consequences.