Fever is an increase in body temperature above what is considered normal (between 35 and 37.5 ° C). Fever arises in response to an infection by bacteria or viruses and acts as an adaptive response that helps the body fight these microorganisms.
Basically, the increase in temperature kills many microbes. So why don’t we just live a little warmer to avoid being permanently infected by them?
The answer to why we don’t raise our body temperature by one or two degrees Celsius in order to preventively defend ourselves against invading microbes is basically that it is too expensive .
As Bill Bryson explains in his book The Human Body , just raising our body temperature by 2 ° C permanently would imply an energy requirement of around 20%:
Our temperature represents a reasonable trade-off between utility and cost (as is the case with most things), and in fact, even our normal temperature is quite effective at keeping microbes at bay. Just think how quickly these begin to swarm and devour us when we die: this is because our inert body decays to a delicious temperature that constitutes a real invitation for them, like a cake left to cool on a window sill.
There is also vasoconstriction to conserve heat and increased heat production through muscle contraction. That is why we sometimes have tremors .