Your turn
Each lab is one step from the video. Press, drag and pick, and see what happens.
Each lab isolates one part of the story. The models are simplified to show the idea.
Tap the buttons and slide the sliders.
Tap cold, music or fear. What happens to the skin on the arm each time?
Cold, fear and a moving song are unrelated stimuli, yet the skin gives the same response. Try all three.
Tap a button. Watch the arm get bumpy!
Drag across the skin or use the slider. What does the muscle do to the hair, and to the skin?
Contracting the arrector pili swings the hair upright and dimples the skin at the pore, so the surrounding skin bulges.
Slide to squeeze. Up goes the hair!
The drawing is a simplified cross-section of one follicle.
Pick a trigger. Follow the signal from the brain down the nerve to the muscle.
Sympathetic nerves fire the muscle directly; adrenaline, a hormone from the adrenal glands, can also help these muscles contract.
Tap a button. Watch the message zoom to the skin!
A simplified map: real nerves branch much more.
Switch between the cat and the human arm, then raise the hair. Which traps more warm air?
Still air insulates. Dense fur traps a thick layer when raised; sparse human hair traps almost none.
Pick the cat or the arm. Slide to lift the hair!
Play the song, then hit the surprise. When do the chills come?
Aesthetic chills cluster at unexpected moments: a jump in loudness, a new instrument, a high note.
Play the song. Then tap Surprise!
One leading explanation; researchers are still studying chills.
Slide the days in the cold. What happens first, and what comes later?
In cold-housed mice, piloerection comes first; within about two weeks the same nerve helps activate hair follicle stem cells.
Slide the days. First bumps, then new fur!
Based on a 2020 study in mice, not humans.
Goosebumps are tiny bumps on your skin. They pop up when you feel cold, scared, or when you hear music you love.
Every hair on your arm has its own tiny muscle. When the muscle squeezes, it pulls the hair up.
The muscle pulls the skin down a little where the hair comes out. So the skin around it puffs up into a bump.
You can't make goosebumps just by wanting to. Your body has an alarm that works all by itself. It says "squeeze!"
A cat's fur stands up to hold warm air, like a puffy jacket. A scared cat puffs up to look big. Your arm hair is too thin to hold much air.
Goosebumps happen when tiny muscles in your skin, one attached to each hair, tighten. These muscles are called arrector pili. As each one contracts, it pulls its hair from lying flat to standing up, and it tugs the skin down right where the hair comes out, so the skin around it bulges into a small bump.136
You don't decide to do this. The muscles are controlled by your sympathetic nervous system, the automatic "fight or flight" part of your nervous system. That's why goosebumps show up when you're cold, scared, excited, or moved by a song, and why you can't simply switch them off.357
Every hair on your body grows out of a small pocket in the skin called a hair follicle. Each hair root is connected to a small smooth muscle, the arrector pili.3 One end is attached to the side of the follicle below the surface; the other end is anchored higher up, near the top of the skin, at a slant.
When the muscle shortens, two things happen at once:
Goosebumps can appear anywhere you have hair, such as your arms, legs or the back of your neck.7 The name comes from the look of a goose's skin after its feathers are plucked. Doctors have fancier names for it: piloerection, cutis anserina (Latin for "goose skin"), horripilation or the pilomotor reflex.56
The arrector pili muscles are wired to nerves of the sympathetic nervous system.35 This system works without you thinking about it and gets your body ready for action when something important happens. When it fires, it sends signals down nerves to the skin, and it also triggers the release of the hormone adrenaline from the adrenal glands, which sit on top of your kidneys. Adrenaline helps tighten the same tiny muscles.6
The same alarm does other jobs too: it can speed up your heart, make your palms sweaty, or give you "butterflies" in your stomach.68 Goosebumps are just the part of that response you can see on your skin.
| Trigger | What's going on |
|---|---|
| Cold | The most common cause. The body's temperature control switches on the reflex to hold in heat.45 |
| Fear | Part of the fight-or-flight response, like a scary film or a sudden noise.56 |
| Awe, pride, excitement | The sympathetic system takes input from brain areas involved in emotion.5 |
| Music or art | "Chills" or frisson, often at a surprising moment in the music.58 |
Keeping a steady body temperature is one of the body's big balancing jobs, called homeostasis. Goosebumps and shivering are two of the ways your body reacts to cold.4 You can read more about it in why homeostasis is important.
Goosebumps make much more sense on an animal with a thick coat. When fur stands up, it traps a thicker layer of still air next to the skin, and still air is a good insulator, a bit like a puffy jacket. The thicker the layer, the more body heat stays in.36 Birds do the same with their feathers (see how penguins stay warm).
Raised fur has a second use: it makes an animal look bigger. A cat facing a dog arches its back and puffs up its fur and tail to seem more dangerous, and a porcupine raises its sharp quills when it senses danger.56 This link to looking scary may explain why the reflex is part of the fight-or-flight system.5 (Cats have other surprising body tricks too; see how cats purr.)
Humans have relatively little body hair, and it's short and thin. Raising it traps almost no air, so goosebumps do very little to keep us warm.16 Scientists think the reflex is mostly a leftover from our much hairier ancestors, and it can still be seen clearly in our primate cousins.58 Our loss of thick body fur is one small part of the long story of how humans evolved.
Musical chills have a name: frisson, from the French word for "shiver". They often arrive at a surprise: a new instrument comes in, a singer hits a high note, or the music suddenly gets louder.8
One explanation, from researcher Mitchell Colver at Utah State University, is that the fast, emotional part of your brain reacts to a sudden new sound as if it might be a threat, and switches on the fight-or-flight alarm. Milliseconds later, the slower thinking part of your brain works out that there's no danger, and the feeling turns into pleasure.8 In his studies, people who score high on "openness to ideas" (curious, imaginative listeners) got goosebumps from music more often.8
A 2011 brain-scan study at McGill University found that listeners' brains released dopamine, a chemical linked to pleasure and reward, at their moments of peak emotion in music they loved.9
For a long time goosebumps looked like a leftover with no job in humans. Then in 2020, a team led by Ya-Chieh Hsu at Harvard, working with Sung-Jan Lin at National Taiwan University, published a study in the journal Cell using mice.12
They found that the sympathetic nerve that makes the arrector pili muscle contract also connects directly to the stem cells in the hair follicle (in a bulge near the muscle), the cells that make new hair. The nerve "talks" to them with a chemical messenger called norepinephrine. The muscle acts like a bridge that keeps the nerve in place: without the muscle, the connection was lost and new hair growth was delayed.12
When mice were kept in the cold, they got goosebumps first. Then nerve activity rose, and the stem cells started making new hairs in less than two weeks.1 As first author Yulia Shwartz put it, it's a two-layer response: quick relief now, and a thicker coat if the cold lasts. The finding could help research on hair loss and wound healing.15
Yes. Goosebumps are a normal reflex and nothing to worry about. Only rarely can goosebumps that keep coming back without any clear cause be a sign of another medical problem, so if that happens, it's worth mentioning to a doctor.57
Keep exploring other things your body does on autopilot: what causes hiccups, how cats purr and why sleep is important.
A tiny muscle attached to each hair follicle, called the arrector pili, tightens. It pulls the hair upright and tugs the skin down where the hair comes out, so the skin around it bulges into a little bump. Your sympathetic nervous system (the automatic fight-or-flight system) gives the order, so you can't switch goosebumps on or off by choice.
The most common trigger is feeling cold. Strong emotions can set them off too: fear, excitement, awe, pride, or being moved by music, a film or a speech. All of these activate the same fight-or-flight system that controls the tiny hair muscles.
Fear is the classic one, but awe, pride, excitement and being deeply moved (for example by music or art) can all cause goosebumps. Musical chills are called frisson, and they often come at a surprising moment in a song, like a sudden loud part or a soaring high note.
Yes. Goosebumps themselves are a normal, harmless reflex. Only rarely, goosebumps that keep appearing with no clear reason can be linked to another health problem, so if that happens it's worth mentioning to a doctor.
In furry animals, raised hair traps a thicker layer of still air next to the skin, which holds in body heat like a puffy jacket. Humans have short, thin body hair, so the trick barely works for us anymore, but our bodies still run the same old reflex.
Many mammals have the same reflex. A frightened cat puffs up its fur and tail, and a porcupine raises its quills. Raised fur keeps animals warmer and also makes them look bigger to an enemy.
One explanation (scientists are still studying it) is that a sudden change in the music makes the fast, emotional part of your brain react as if something important or risky is happening, which sets off the fight-or-flight alarm. A moment later your thinking brain realises you're safe. A 2011 brain-scan study found that people release dopamine, a feel-good brain chemical, at their peak moments of pleasure in music.
This page explains how the body works; it isn't medical advice.