1.Progressive period: Many febrile diseases may not have symptoms in this period. The duration of symptoms in this period varies according to the specific conditions of the febrile disease, mainly manifesting as: general malaise, fatigue, back and limb pain, headache, loss of appetite, mental instability, and low fever; some rash diseases may have a prodromal rash before the appearance of a general rash, such as the prodromal phase of measles, the oral mucosa may appear as Fick’s spots. 2, body temperature rise period: This period is characterized by more heat production and less heat loss, so heat production is dominant, so the body temperature rises. After the pyrogen enters the body, the excitability of the thermoregulatory center is changed, causing the patient’s skin vasoconstriction and reduced sweating. At the same time, due to the enhanced metabolism in the body, as well as the reflexive contraction of the erector spinae muscle due to cold sensation, and the contraction of muscle groups to form chills can increase heat production. The clinical manifestations are pale, dry, sweatless skin, “goose bumps”, and a cold sensation when touching the child’s skin; if chills occur, it is a sign that hyperthermia will occur. In young children, convulsions may occur in this case. During chills, the body temperature is mostly above 38℃, and most of them reach the extreme stage of hyperthermia within a few hours, such as malaria, lobar pneumonia, sepsis, drug-reactive fever, etc. The above are those with sudden rise in body temperature. Gradual rise in body temperature refers to those who have low fever at the beginning of the fever and gradually rise from low fever to high fever within a few days, which is called gradual rise in fever. Most of them do not have chills, but sometimes they can feel cold, such as atypical typhoid fever. Some have a sudden rise in fever, which may start as a low fever that is ignored. In addition, wave fever, tuberculosis and other diseases show a gradual rise in temperature fever. 3, high temperature persistent period: At this time the body temperature has reached its peak, this period is characterized by the heat dissipation process began to enhance, the thermoregulatory center constantly strengthen the regulatory role. As the heat dissipation process begins to enhance, the patient’s body surface skin vasodilatation, respiration strengthens, and sweating begins, so that the body temperature does not continue to rise. However, since the body is still stimulated by thermogenic substances, the heat production does not decrease, so the relative balance between heat production and heat dissipation is re-established on a new basis, and the body temperature is maintained at a certain high level. The clinical manifestations are flushed and burning skin, accelerated and strengthened breathing, sweating, etc. The high fever in this period can last for a few hours (such as malaria) or days (such as pneumonia), or even more than a few weeks (such as typhoid fever). 4, the period of falling body temperature: This period is the end of the fever. It is characterized by the predominance of the heat dissipation process and the return to normal body temperature. Due to the body’s defense or appropriate treatment, the role of pyrogen in the body gradually disappears or weakens, heat production decreases, while heat dissipation is still at a high level through the regulation of the thermoregulatory center, the patient’s body surface skin vascular expansion, a lot of sweating, heat dissipation strengthens, so the body temperature begins to fall, heat production and heat dissipation finally return to a normal relative balance. The way the body temperature drops is generally gradual, that is, the body temperature gradually returns to normal within a few days (such as typhoid fever); there are also abrupt reductions, that is, the body temperature drops to normal or even below normal within a dozen hours or less (such as lobar pneumonia). When the body temperature drops, a large amount of body fluids are lost due to heavy sweating, so caution must be exercised when using antipyretics for patients with high fever and children to prevent deficiency and other complications.