Why can a fever cause chills?
Short answer
A fever can cause chills because the hypothalamus temporarily raises the body's temperature set point. Until the actual temperature reaches that new target, the body feels cold.
What changes when the set point rises?
When the immune system responds to an infection or another cause, signals can act on the hypothalamus and raise the set point. The body then tries to close the gap between its current temperature and the new target.
One response is to constrict blood vessels near the skin, which reduces heat loss. This can make the hands and feet feel cold while the body is trying to conserve heat at its center.
Why do muscles shiver?
Rapidly tightening and relaxing muscles is one way to produce heat. Even when a thermometer reading has started to rise, a person may feel chilled or shiver until the body reaches the higher set point.
What happens when a fever breaks?
When the cause settles or the set point returns to normal, the body begins to release heat. Skin blood vessels widen and sweat can evaporate from the skin, so sweating is common as a fever comes down.
Is fever the same as hyperthermia?
No. A fever involves a raised temperature set point. Hyperthermia can occur when heat builds up from a hot environment or strenuous activity without the set point being raised. The causes and responses differ, so severe symptoms should not be watched at home based on the label alone.
When should someone seek medical advice?
Chills alone cannot identify the cause. Seek medical advice promptly for breathing difficulty, confusion, a stiff neck, seizures, signs of dehydration, or a fever in an infant. It also helps to report the person's age, how the temperature was measured, and other symptoms.