A body temperature of 37.7°C is a state of hypothermia. A variety of diseases can cause fever, and the duration of fever and specific symptoms should be considered to make treatment for specific causes. Fever is a normal physiological response of the human immune system to resist various pathogenic microorganisms. Although some environmental and personal factors can cause a temporary increase in body temperature, it will not cause huge fluctuations in body temperature, and if the difference in body temperature exceeds 1℃ in a day, it can be clearly considered as fever. If a person with normal body temperature suddenly has low fever, it may be caused by bacterial infection or viral infection, such as cold, pneumonia, bronchitis, etc. If the fever is low for a long time, it may be caused by tuberculosis, liver disease, chronic bile duct infection, rheumatoid arthritis, rheumatoid arthritis, etc. For long-term low fever, it is recommended to go to a hospital for examination to determine the specific cause. In case of sudden low fever, physical cooling can be done first and it is not recommended to take fever-reducing drugs at will.