Right now I’m fighting off a meanie-head bacterial infection with my trusty bottle of Zinthromax and my personal therapy tool, the SDMB. But the most miserable part isn’t the sore throat, the phelgm, or the fever – it’s the aches and pains. Why in the world do my legs hurt? And my shoulders? What’s up with that, anyway?
So, MediDopers, I’m posing this question to you: why does my body ache when I’m sick?
I’ll try to keep this simple.
When you have an infection, the body is generally pretty good at realizing that there are some “foreign bodies” around. Your immune system ramps itself up and tries to fight off the infection. It does this by making several types of white blood cells which help kill, “eat” and pacify infected cells. Several chemicals, include interleukins and cytokines, are released by cells to signal for help and fight off the infection. Several of these chemicals are “inflammatory mediators” which make the blood vessels leakier and cause pain and fever.
Many illnesses, including most infections, are associated with inflammation – a process that generally involves redness and swelling (due to increased blood supply), tenderness (due to pain chemicals), heat or fever (largely due to a chemical called IL-1) and possibly “loss of function” at the cellular level.
Diffuse muscle pain, as in a flu infection, is a by-product of the chemicals used to signal the body to help fight the infection. Pain has an important function in protecting you by telling you not to do stuff that can cause more damage. Of course, pain is also a pain.
I’d be pleased to make this much more complicated. 
Thanks [B}Dr_Paprika**
If the pain signal is a mechonism to get us to ‘take it easy’ I wonder why the signal isn’t more like a feeling of sleepyness.
Is it just psychological that flu pain feels like it is in my bones, or is the pain chemical actualy concentrated or detected in my bones?
I actually wonder sometimes why we try to combat these natural responses that sometimes cause pain. Our bodies usually know what they’re doing, correct? For example - lets say I break my ankle. Well I could go take a ton painkillers and walk around on that ankle just fine, but it wouldn’t be too good for the healing process, would it? This is why I try to avoid taking any painkilling medication if I can, and only take 1 aspirin at that (others in my family like to pop in 2 or 3 right off the bat).