Goosebumps

How it works

Every hair on your body sits in a follicle, and a tiny strip of smooth muscle is attached to it. This is the arrector pili muscle². When it contracts, it tilts the hair upright and pulls on the skin around it. The skin dimples into a small bump. Across an arm or a leg, thousands of these bumps appear at once¹.

The muscles are driven by the sympathetic nervous system, the fight-or-flight system. You cannot choose to fire them, except for a few unusual people¹. Three kinds of trigger set them off¹:

• Cold. The skin senses a drop in temperature.
• Fear or shock. A sudden threat, a loud sound, or a fright.
• Strong emotion. Music, a speech, a film scene, or a memory. This version is called frisson, and it often comes with a shiver down the back³.

In a furry animal all of this makes sense. Raised fur traps a thicker layer of still air next to the skin, which keeps the animal warm. Raised fur also makes the animal look bigger to an enemy. A cat facing a dog does exactly this¹. Humans have kept the muscles and the nerves but lost most of the fur. The reflex still fires, but the effect is now almost nothing. That makes it a vestigial trait, a leftover from ancestors¹.

The name comes from the look of a plucked goose. The Latin term cutis anserina means the same thing¹.

History and culture

Many languages name the effect after a plucked bird. In French it is chair de poule, chicken skin. In Japanese it is torihada, also bird skin¹. A small number of people can raise goosebumps at will, with no cold or emotion involved. This is covered in its own entry.