Why do people get a fever when they're sick?

You've already got a relentless cough, your head is pounding and it's impossible to breathe through the nose. All you need now is this, a fever. A certain part of the brain called the hypothalamus is responsible for whether someone experiences fever or not. This area of the brain regulates human body temperature, which is normally just below 37 degrees centigrade. The hypothalamus works like a climate control system. It can change the temperature as needed. If it's too warm, it lowers the temperature. If it's freezing cold, the push of a button warms things up again. When the common cold is accompanied by fever, the hypothalamus can drive the temperature way up. Thirty-nine degrees centigrade or more is no rarity.

Here's what happens: If pathogens enter the organism, the immune system reacts immediately to these foreign bodies. A variety of semiochemicals called pyrogens are released. The bloodstream carries the pyrogens to the brain, to the hypothalamus. When they arrive they trigger a chain reaction signalling to the hypothalamus that the body temperature has to be increased. As a result the muscles begin to shake, causing what we call the shivers. This rapid movement warms the body and the temperature increases. While the fever is debilitating the ill person and confining them to bed, the pathogens in the person's body are also beginning to have difficulties of their own. This is because they do not thrive in high temperatures. The fever prevents these intruders from multiplying any further. While all this is going on, the human immune system is at battle stations. Antibodies destroy the weakened pathogens and things begin to get better. The human internal climate control system not only makes the person who is ill feel weak, it also repels the pathogens. The patient gets better. Fever - it's a process of changing the temperature to heal an entire organism - a simple principle that's better than any chemical remedy.