Why Does Your Body Start Shivering When You're Cold?

Every time a muscle works, it gives off a large share of its energy as heat. That's also why you warm up when you exercise. Shivering takes advantage of this. Muscles that pull in opposite directions take turns tightening several times a second, so your arms and legs only shake in place, and almost all the energy spent is left over as heat.

That heat adds up. Studies show that when you shiver hard, the heat your body produces can rise to several times what it makes at rest. Chattering teeth come from the same thing: your jaw muscles shivering in the same way.

Your body doesn't jump straight to shivering. First it narrows the blood vessels in your hands, feet and skin so less heat escapes to the outside. On a cold day, that's the stage when your fingertips turn pale and cold first. If that still isn't enough to hold your core temperature, shivering begins. Curling up and folding your arms without thinking when it's cold serves the same purpose: it shrinks the surface exposed to the air so you lose less heat.

A common misconception is that shivering means your body is too weak to handle the cold. In fact, it means your body is doing its job of protecting its temperature. When you're coming down with a cold and get the chills even in a room that isn't cold, it's because your body has briefly raised its target temperature, so your current body temperature feels cold to it.

Shivering uses a lot of energy, so your body can't keep it up for long. That's why you feel unusually tired and hungry after shivering in the cold for a while. Once you start shivering, the quickest help is to take off wet clothes, get out of the wind and warm up with a hot drink. Covering your head and neck with a hat or scarf also cuts down the ways heat leaks out.

There's one thing to watch for. When the body gets very cold, shivering can actually stop. If someone who has been in the cold for a long time stops shivering and suddenly goes quiet, slurs their words or seems drowsy, it may be a sign of greater danger, not that they've recovered.