What is shivering? It is a really fast contraction and relaxation cycling of muscles. The cause of shivers is your hypothalamus. It sends a signal to your muscles via your nervous system to get contracting rapidly. And goosebumps often precede a shiver episode.
Shivering muscle action is uncontrollable because it’s a reflex. Reflexes are involuntary. Try as you might, ultimately you can’t will your shivers to stop. Why your hypothalamus jerks you around this way is for body heat.
Why you shiver is to raise your body’s core temperature. Shivering is a method of heat production. When your hypothalamus detects a temperature drop below a set point it automatically kicks the shiver reflex. Under healthy conditions, this set point is somewhere around 98.6 for most.
Normally, being in the cold is what causes you to shiver. And usually you can gain control over these shivers by changing your circumstances, for instance putting on warmer clothes or getting out of the cold by seeking shelter.
However, another reason you may be shivering is fever. Why? Because a fever that develops with an immune system response can secrete a pyrogen. A pyrogen causes your body’s temperature set point to rise. A higher set point causes shivers even though the ambient air temperature is comfortable for everyone else. Health conditions that typically instigate fever related shivers are bacterial or viral infections.