Fever is the most common symptom of illness in children. Parents often wonder why their children’s hands and feet are sometimes hot when they have a fever, but sometimes they have cold hands and feet instead. Some parents would call cold hands and feet “internal heat” and hot hands and feet “external heat” is this really the case? This starts from the mechanism of fever, humans are constant temperature animals, under normal circumstances, the body’s heat production and heat dissipation is in a state of balance, such a state can maintain our body temperature fluctuates between about 36 ℃ – 37 ℃. When the pathogen invades the child’s body, the pathogen as an external thermogenic source, as well as after the invasion of the body, the body struggle with the pathogen produced by some inflammatory products as a thermogenic source, affecting the central body temperature adjustment point, the body will consider the temperature of about 36.5 ℃ is abnormal, think that 39 ℃ or higher body temperature is reasonable, so mobilize the whole body to increase heat production and reduce heat dissipation to achieve a higher body temperature. One of the ways of heat production is the movement of skeletal muscles, so there will be the shaking and shivering of limbs that we see, and in order to reduce heat dissipation, the body will contract the peripheral blood vessels, so there will be cold hands and feet, and at the same time, the body will be afraid of cold and will naturally want to wear more clothes to relieve the cold feeling, which is also a way to reduce heat dissipation. At this time, the capillaries in the hands and feet will stretch again, and heat production will again be equal to heat dissipation, so we will feel that the child’s whole body is hot, including the palms of the child’s hands and feet. Therefore, during the stage of rising body temperature, the child’s hands and feet are often cold. The faster the body temperature rises, the more obvious this phenomenon of cold hands and feet becomes, and when the body temperature rises to the plateau, the hands and feet will become hot. The cool or hot hands and feet we see are just different periods of fever, and have no other special meaning. It has nothing to do with “internal heat” or “external heat” as some parents say.