Shivering is a bodily function in response to cold in humans and is caused by your muscles tightening and relaxing in rapid succession. This involuntary muscle movement is your body’s natural response to getting colder and trying to warm up. When the core body temperature drops, the shivering reflex is triggered to maintain homeostasis. Skeletal muscles begin to shake in small movements, creating warmth by expending energy.
Located in the posterior hypothalamus near the wall of the third ventricle is an area called the primary motor center for shivering. This area is normally inhibited by signals from the heat center in the anterior hypothalamic-preoptic area but is excited by cold signals from the skin and spinal cord. Therefore, this center becomes activated when the body temperature falls even a fraction of a degree below a critical temperature level.
Increased muscular activity results in the generation of heat as a byproduct. Most often, when the purpose of the muscle activity is to produce motion, the heat is wasted energy. In shivering, the heat is the main intended product and is utilized for warmth.Babies don’t shiver when they’re cold because they have another temperature-regulation response. Babies actually warm up by burning fat in a process called thermogenesis. It’s similar to how hibernating animals survive and keep warm in the winter.
Some of the common causes:
A drop in your blood sugar levels can trigger a shivering response. This can happen if you haven’t eaten for a while.
When you shiver, but you don’t feel cold, it could be a sign that your body is starting to fight off a viral or bacterial infection. Just as shivering is your body’s way of warming up on a chilly day, shivering can also heat up your body enough to kill a bacteria or virus that has invaded your system.
Strong emotions can cause a person to shake or shiver. This is often due to a surge of adrenaline in the body. Adrenaline is a hormone that triggers the body's fight-or-flight response.
For some people, stress or mental health factors can cause shivering and other involuntary movements.
Involuntary trembling, shaking, or shivering can be due to a medical condition called essential tremor. Essential tremor is a neurological condition, meaning that it relates to the brain.