Why We Get Goosebumps

You step out of a warm shower into a cold bathroom. Suddenly, your arms are covered in tiny bumps. The hairs on your skin are standing up. In English, we call these bumps goosebumps, because they make our skin look like the skin of a bird without its feathers. But why does our body do this?

Every hair on your body grows out of a little hole in the skin. Attached to each one is a tiny muscle called an arrector pili. When that muscle gets shorter, it pulls the hair up straight. The skin around it rises into a small bump. You can't decide to do this. It's controlled by the part of your nervous system that works automatically. That's the same part that makes your heart beat faster when you're in danger.

The muscles usually react to two things: cold and fear. For animals with thick fur, both reactions are very useful. If a cat or a bear feels cold, its raised fur traps a layer of warm air next to the skin, like a coat. If an animal feels threatened, its fur stands up and makes it look bigger. That might scare an enemy away. You've probably seen an angry cat do this.

Humans lost most of their fur a long time ago, but we kept the reflex. That's why we still get goosebumps when we're cold, even though our short hairs can't keep us warm. And it's why the skin on our arms reacts when we hear a strange noise in a dark house.

There's a third thing that can cause goosebumps, and it's much more surprising: music. Many people get them when a song does something they don't expect, like a sudden change in volume, a very high note or an unusual chord. Scientists who study this reaction, sometimes called "frisson," think that the brain treats the surprise like a small alarm at first. Then it quickly understands that there's no danger, and the alarm turns into pleasure.

So the next time it happens, you'll know what's going on: tiny muscles, an old reflex and a brain that loves a good surprise. Now think about it: which song gives you goosebumps?