Many people have had the experience of fever (proverb: fever), some are low fever, some are high fever, some quickly well, some may not get better for a long time, this time often people ask: a simple fever, how this difficult to get? In fact, doctors are most afraid of the cause of fever to be investigated, because there are many kinds of fever. First of all, we have to understand what is fever? Fever refers to the direct effect of pyrogen on the thermoregulatory center, dysfunction of the thermoregulatory center or a variety of reasons for excessive heat production, heat dissipation is reduced, resulting in an increase in body temperature above the normal range of cases. Specific performance: when the axillary temperature exceeds 37.3 degrees, oral temperature exceeds 37.6 degrees, anal temperature exceeds 37.9 degrees can be diagnosed as fever. Body temperature of 37.3-38 ℃ is low fever, 38-39 ℃ is medium fever, more than 39 ℃ is high fever, more than 41 ℃ is ultra-high fever.