A healthy person's normal body temperature usually fluctuates between 97°F (36.1°C) and 100°F (37.8°C), with the average being 98.6°F (37°C). When our body temperature rises above 98.6°F, we call it fever. But why does the body temperature rise during fever?
Our normal body temperature is maintained by a regulatory center called the “anterior hypothalamus”, located deep within the brain. This region functions like a thermostat, registering body temperature. The nervous system constantly relays information about the body's temperature to the thermostat, which in turn activates different physical responses designed to cool or warm the body, depending on the circumstances in order to maintain the body temperature at a normal set point.
Fevers are primarily caused by viral or bacterial infections. So, when an infection occurs, fever-inducing agents called pyrogens are released in the bloodstream, either by the body's immune system or by the invading cells themselves. These pyrogens trigger the resetting of the thermostat at a higher level and we thus register a higher body temperature during fever.
To reach a higher temperature from the normal body temperature, the body moves blood to the warmer interior, increasing the metabolic rate, and inducing shivering. The "chills" that often accompany a fever are caused by these movements of blood to the body's core, leaving the surface and extremities cold. Once the higher temperature is achieved, the shivering and chills stop. Again, when the infection is overcome or drugs such as aspirin or acetaminophen are taken, the thermostat resets to normal (i.e. 98.6°F) and the body's cooling mechanisms send the blood back to the surface and sweating occurs.
We often panic when we have high temperature or fever. But on the contrary, fever is an important component of our immune system. Actually, the immune system chemicals that react with the fever-inducing agent and trigger the resetting of the thermostat, increase the production of cells that fight off the invading bacteria or viruses. Higher temperatures also inhibit the growth of some bacteria, accelerating the chemical reactions that help the body cells to repair themselves. In addition, the increased heart rate that may accompany the changes in blood circulation, also speeds up the arrival of white blood cells to the site of infection to fight with the invaders.