Fever is diagnosed when the body temperature is higher than normal. The body temperature can be measured at the armpit, mouth and anus, and the normal body temperature is measured as follows: the armpit temperature is 36.0-37℃; the mouth temperature is 36.3-37.2℃, and the anus temperature is 36.5-37.7℃. Body temperature higher than the normal range can be judged as fever. On the basis of the judgment of fever, the fever can also be graded. Taking the oral temperature as an example, it can be determined after measuring the oral temperature: low fever is 37.3-38.0 ℃, medium fever is 38.1-39.0 ℃, high fever is 39.1-41.0 ℃, and ultra-high fever is greater than 41.0 ℃. Human body temperature is not fixed, body temperature can fluctuate with gender, age, day and night, exercise, emotions and measurement methods and other factors, but this change is often within the normal range, generally within 24 hours of body temperature fluctuations of no more than 1 ℃. Physiologically, the body temperature is slightly lower in the morning, slightly higher in the afternoon, slightly higher after exercise, eating, before menstruation in women or during pregnancy, and slightly lower in the elderly. When measuring armpit temperature, it is recommended to sterilize the thermometer in advance and keep your emotions stable. Sweating should be wiped away from the armpits before measurement. If bathing, the temperature should be measured only after 20 minutes, and the thermometer should be in full contact with the skin, with no other heat sources around to interfere. When measuring oral temperature, it should be noted that the measurement should be taken half an hour after eating, drinking or smoking. Care should be taken to avoid biting the thermometer, and oral temperature measurement is not recommended for children. When measuring rectal temperature, care should be taken to apply a small amount of lubricant to the mercury end first, but anal temperature is not recommended for people with anorectal diseases, and it is also recommended to perform this operation for the first time under the guidance of a doctor.