Shivering

body science · staying warm · reflex

Muscles shake for warmth. When you get cold, your muscles start twitching super fast in tiny movements. All that shaking burns energy and creates heat to keep your core body temperature up, like a built-in furnace.

Your brain is the thermostat. A part of your brain called the hypothalamus watches your body temperature like a careful guard. When it senses you're too cold, it sends signals telling your muscles to start shivering.

Fever feels weird and cold. When you have a fever, your hypothalamus actually raises the temperature setting it wants your body to reach. So your body shivers to heat up, even though you already feel hot to everyone else.

All warm-blooded animals do it. Mammals and birds shiver when they're cold, from tiny mice to huge elephants. It's one of nature's most reliable ways to stay alive in freezing temperatures.

Fear can trigger shivering too. Extreme fear can make you shiver because your body goes into survival mode, the same way it does when you're freezing cold.