There are several reasons for not having fever for many years, including good physical quality, hypothermia, damage to the brainstem thermoregulatory center, etc., as follows: First, good physical quality: usually strong immunity, while focusing on disease prevention, no various diseases occur, or due to strong body immunity, even if various infections occur, but the symptoms are mild, and the body’s immune cells can clear the pathogens and No clinical symptoms appear, but only a recessive infection. Second, hypothermia: In the elderly and immunocompromised people, the thermoregulatory center is hypothermic, and the body temperature is not sensitive to various internal or external factors that cause the body temperature to rise. Third, the brainstem thermoregulatory center is damaged: intracranial lesions make the brainstem thermoregulatory center damaged, unable to regulate body temperature, so that the body temperature can not show diurnal fluctuations, and can not appear to various infections hyperthermia phenomenon.