One of the main reasons that our body aches when we are sick, like with a cold, is that the body’s immune system is producing plenty of antibodies in addition to the effects of all those viruses replicating in our cells killing them and leaving the area ‘raw’ and exposed.
These antibodies also promote the release of histamine which typically dilates (widens) blood vessels near an infection, this allows for more of the body’s defenses to get at the infection. There are histamine receptors in blood vessels that cause them to dilate.
As these chemicals are released into the blood stream they can end up in the muscles or other body parts. Various body systems can have receptors to histamine that can then trigger a pain receptor.
In addition to histamine there are biochemicals called cytokines that are released when the body has an immune response that are also known to trigger a biochemical pathway that can affect pain receptors.
Histamine and cytokines releases can change the perception of pain receptors in the body making them more sensitive to pain factors.
There are other factors that come into play also such as biochemicals called interleukins that relate to fever conditions and temperature increases, all of which can affect pain receptors in different ways, for example heat receptors.
The overall perception of pains and aches over the whole body can vary from person to person and there may be other combinations of psychological, physiological or even nutritional factors that may influence this.