What are fevers anyway? Why do our bodies suddenly turn up the heat when we get sick? Typically, our internal temperature is 98.6 degrees Fahrenheit (37 degrees Celsius). That can vary by a degree up or down depending on the time of day. Often it goes down a degree just before sunrise and up a degree sometime after lunch.
That's a pretty stable interior climate zone. But it can change. If your immune system stumbles across trouble somewhere in your body, it sounds the alert. Biochemical materials called pyrogens start flowing through your bloodstream. Both body tissues and certain pathogens produce these pyrogens. The "pyro" in pyrogen is not a coincidence. "Pyro" comes from the Greek word for "fire." When these pyrogens reach the base of the brain, they run into the hypothalamus, which happens to be in charge of your body's temperature settings.
Detecting pyrogens, the hypothalamus dials up the heat and tells the body not to let it out. Luckily the viruses and bacteria that make us sick are heat-sensitive. The idea is to make things hot enough to cook the bacteria or viruses until they're dead. Seems like a good idea as long as our internal organs don't get baked along with the pathogens. That's actually a possibility. Sometimes in its efforts to get rid of the stuff that's making us sick, our immune system can make us even sicker. If our temperature tops 105 degrees Fahrenheit (40.5 Celsius) for too long, we can be in danger of side effects such as seizures and tissue breakdown [source: Nalin].
Kids tend to have higher fevers that spike more quickly because their immune systems are young and inexperienced. Think of your childhood hypothalamus as a trigger-happy rookie cop and your grown-up hypothalamus as a jaded old hand who does the minimum necessary.
So much for fevers. What about dreams?