Why do we shiver when we are cold?

When sensors in the skin and brain detect a drop in temperature, the hypothalamus triggers shivering — quick, rhythmic muscle contractions that burn energy and release heat. This can increase heat production by about five times the resting rate. Blood vessels in the skin also constrict to keep warm blood near the core organs. If the body keeps cooling, shivering becomes more intense. In severe hypothermia, shivering eventually stops, which is a dangerous sign. Shivering can also occur briefly during a fever, when the hypothalamus resets the body’s thermostat higher and the body feels cold relative to the new set point.