A body temperature of 38℃ belongs to a low fever state, which can be caused by a variety of diseases, and should be treated according to the cause by considering the duration of fever and specific symptoms. Fever is a normal physiological response of the body’s immune system to resist various pathogenic microorganisms, although environmental and personal factors can lead to a temporary increase in body temperature, but it will not cause large fluctuations in body temperature. If a person with a normal body temperature suddenly develops a low fever, it may be caused by bacterial or viral infections related to colds, pneumonia, bronchitis and other diseases. If the fever is prolonged, it may be caused by tuberculosis, liver disease, chronic bile duct infection, rheumatoid arthritis, rheumatoid arthritis and other diseases. People with long-term low fever should go to the internal medicine department of the hospital to check the specific cause. If the fever is suddenly low, physical cooling can be carried out first, and then medication can be applied when other symptoms appear.