If fever is a natural immune defense, why do people take drugs to lower it?
Q: If fever is a natural defense against pathogens, why do sick people take NSAIDs to reduce the fever?
Personal comfort is the primary answer. Quite a bit of research has gone into fevers, and the current consensus is that Fevers less than 105F (40.5C) shouldn't necessarily be treated.
The primary reason the body raises its temperature (via the Hypothalamus in this case) is that bacteria and viruses tend to optimally thrive at 98.6F, which is also your body's optimal operating temperature. By raising the body's temperature, the bacteria/viruses become less efficient, allowing your body to "catch up" since the body's immune response takes time to ramp up before it reaches its peak (which is a bit after peak viral/bacterial load). Here's an example for Hepatitis (HBxAg = the virus, Anti-HBx = antibodies against the virus):
Along with the Fever, joint inflammation (part of the Innate Immune system's primary response) is also a coinciding symptom. So when your body begins to fight an infection you get a fever (which can make the environment uncomfortably hot/cold) and the tissues around your joints swell (which makes movement and relaxation uncomfortable). NSAIDs like Ibuprofen reduce those symptoms, making the duration of the infection more bearable. They do not reduce the length of the infection by any measure (and might increase it, though the research is not particularly conclusive), but can make the day go by better if you've used up all your sick days or have a child to take care of.
Basically, people take NSAIDs to reduce fevers for the same reason most take any over-the-counter pain medications. To make life a little easier in the meantime.
First question: Yes. The immune system releases pyrogenic cytokines such as IL-1. Bacteria aren't typically used to 37C, they prefer working at under that temperature to function in the environment. Our body however can take a few degrees here or there however this severely compromises the bacterial enzyme activity. The same is true for other pathogen enzymes. The body also increases copper concentrations in the blood for similar reasons. Problem is of course if the body goes into overdrive and raises our temperature too much, this compromises our own ability to fight the infection so in that case antipyretics like paracetamol can reduce fever.
Second question. It isn't a side effect, however paracetamol works by blocking things like IL-1 that raise temperature. How IL-1 raises your temperature is quite interesting, it tells the hypothalamus (our thermostat) that it should be set higher. So we feel cold (so we try to keep ourselves warm) and the body thinks it's cold (so it increases the temperature by burning glucose mainly)
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