How does a fever develop?

Fever is your friend: Fever is an amazing ability of the body to try and 'fight' something -usually an infection. It actually gives us a survival advantage, and that is why it evolved. There are complex regulations of fever (as with most things in the body). The brain (preoptic area of the anterior hypothalamus) is where the thermostat is located. If you have a fever, it's good to know the cause - a doctor can help.