Why do we shiver?

Shivering is a special way the body has of trying to warm up when it gets cold. Whenever your muscles are working, they are also giving off heat. You already know this because when you are running or playing hard you get warm. Then your body sweats, and this helps cool you by evaporation of the sweat.

When your body gets cold you can help it warm up by running or some other kind of exercise. If you do not do that, your body has its own automatic or reflex way of making muscles work just under your skin. That is what we call shivering.