Medical term, also known as fever. A regulated temperature increase (more than 0.5°C) caused by the upward shift of the thermoregulatory point due to the action of a thermogenic agent is called a fever. Normal body temperature varies slightly from person to person and is influenced by many factors (time of day, season, environment, menstruation, etc.). Therefore, the best way to determine if you have a fever is to compare it with your usual body temperature under the same conditions. If you do not know your original body temperature, an axillary temperature (tested for 10 minutes) of more than 37.4°C can be considered feverish. The normal human body temperature is generally 36 to 37℃, and the oral body temperature of adults in the quiet state in the early morning is 36.3 to 37.2℃; the internal anal body temperature is 36.5 to 37.7℃; and the axillary body temperature is 36 to 37℃. According to the body temperature condition, fever is divided into: low fever: 37.4～38℃; moderate fever: 38.1-39℃: high fever: 39.1-41℃; ultra-high fever: more than 41℃. The cause of fever: fever is due to fever activators acting on the body, which leads to the production of endogenous pyrogen (EP) and into the brain to act on the thermoregulatory feedback diagram of the thermoregulatory center, which in turn leads to the release of febrile central mediators and then causes changes in the tuning point, eventually causing fever. The common fever activators are exogenous pyrogens from outside the body: bacteria, viruses, fungi, spirochetes, malaria parasites, etc.; from inside the body: antigen-antibody complexes, steroids, etc. The endogenous pyrogen (EP) comes from the EP-producing cells in the body, which mainly include: interleukin-1 (IL-1), tumor necrosis factor (TNF), interferon (IFN), interleukin-6 (IL-6), etc. EP acts on the thermoregulatory center located in the POAH, resulting in the production of positive and negative regulatory mediators. The latter can cause a change in the point of regulation and eventually lead to the development of fever. Fever is not a disease per se, but a symptom. In fact, it is one of the body’s mechanisms to fight infection. Fever may even have its uses: shortening the duration of illness, enhancing the effectiveness of antibiotics, and making infections less contagious. These abilities should counteract the discomfort experienced with a fever.