ELI5: Why does your body kill bacteria etc. with high fever when it’s dangerous to yourself?

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Your body is betting that his own regeneration and recuperation mechanisms are better than that if the bacteria, which is most of the cases true. Chemo works similar. It damages everything in your body, but since cancer has accelerated cell growth and divisions, it affects the cancer more than you. Imagine putting an enemy with you in an airtight room, because you are pretty sure you can hold your air longer and he dies first.


The body can handle it far better than the bacteria or viruses can. In addition, a low grade fever isn’t particularly dangerous. Whenever you get a fever high enough to actually be dangerous, that’s when the disease is so bad that if the fever doesn’t work, you are dead anyway. You can’t get deader than dead, so killing you with a fever doesn’t actually cause any harm. Or wouldn’t if modern medicine didn’t exist. But your body is optimized in most way for before medicine existed, so sometimes the way the body works, which would be great in the hunter-gather days is bad for you in modern life.


The body keeps a pretty tight control over its temperature, even with a fever. A fever on its own isn’t dangerous and is beneficial in controlling the infection; of course fevers *can* be dangerous when they get out of control, which typically happens with severe illness. The way it helps is in a few ways: The increase temperature helps certain immune cells move and function better. It helps T cells (a type of immune cell) reproduce more. It also helps to decrease the effectiveness of certain toxins that bacteria release that cause us harm and cause many effects of illness.


Fever is a natural defense mechanism against any foreign substance. A “low” fever (38-39°C) is safe. Because it will increase the bloodflow so that immune cells can arrive faster at the foreing substance. Higher metabolims so more energy is available for repair etc. The danger of fever starts when it hits >40°C because at that point our proteins will start to break down.


Basically your body is just trying to make itself as hard to live in as possible so it raises the body temperature and starts depriving itself of certain minerals in order to starve the bacteria out and slow their spread.