Why Do We Get Goosebumps? The Science of Chills

Step outside on a cold morning, watch a tense scene in a horror film or reach the chorus of a favourite song, and the hairs on your arms suddenly stand up as your skin breaks out in tiny bumps. That familiar feeling is a reflex millions of years old — and a reminder that humans were once much hairier creatures.

The tiny muscle that raises your skin

At the base of almost every hair on your body sits a muscle too small to see: the arrector pili. One end attaches to the hair follicle, the pocket that holds the hair root, and the other to the upper layer of the skin.

When the muscle is relaxed, the hair lies at an angle against the skin. When it contracts, it:

1. Pulls on the hair root and stands the hair upright.
2. Pushes the follicle upwards, raising the skin around it.
3. Creates a little dimple and bump around each hair — the “plucked goose” look that gives goosebumps their name.

We do not control these muscles. They are switched on by the sympathetic nervous system, which runs involuntary functions such as heart rate and digestion. The sympathetic system is also the centre of the body’s “fight or flight” response, which is why our hair stands on end when we are frightened.

Two jobs inherited from furry ancestors

To see what goosebumps are really for, look at furry animals. In them the reflex does two important things.

Insulation

When fur is fluffed up in the cold, it traps a layer of still air between the hairs. Air conducts heat poorly, so this layer slows the loss of body heat, much like a down duvet. Birds and cats that look puffed up in winter are using exactly this insulation.

Intimidation

When a frightened or threatened animal raises its fur, it looks bigger than it really is. A cat arching its back with bristling fur, or a porcupine raising its quills, sends a clear message: “Don’t mess with me.”

During evolution humans lost most of their thick body hair, but the nerves and muscles controlling the reflex stayed. So when we get goosebumps today, we neither warm up nor look scarier — our body simply keeps running the old program.

A new finding: more than a leftover?

For many years human goosebumps were seen as a useless evolutionary remnant. In 2020, a study by Ya-Chieh Hsu and colleagues at Harvard University, published in Cell, nudged that view.

Working with mice, the researchers discovered that:

• The arrector pili muscle acts as a bridge that lets a sympathetic nerve reach the hair follicle.
• The sympathetic nerve does not just contract the muscle; it also connects directly to stem cells in the hair follicle.
• During prolonged cold, these nerves stimulate the stem cells and kick-start new hair growth.

So the same system that raises hairs for instant insulation may, in the longer term, help the coat grow thicker. These findings come from mice, and how far the same relationship holds in human skin is still being investigated.

Emotional chills: why does music give us goosebumps?

Perhaps the most intriguing kind of goosebumps are the ones we get at the climax of a song or during a moving film scene — when there is no cold and no real danger. Scientists call this experience frisson, French for “shiver”.

In a 2011 study at McGill University, volunteers listened to music that gave them chills while their brains were scanned. The results showed that:

• As the music built towards its peak, dopamine release rose in brain regions linked to anticipation.
• At the moment of the chill, dopamine rose in regions at the heart of reward and pleasure.

Dopamine is a brain chemical released during pleasurable experiences such as eating or receiving a reward. Music, despite not being a tangible reward, can activate a similar system. Chills often arrive with an unexpected change in harmony, a sudden rise in volume or the surprise entrance of a new voice.

Not everyone experiences this equally. Research suggests that people who are more open to new experiences get musical chills more often.

How the body really keeps warm

In humans, goosebumps do little to keep us warm. The body has much more effective defences against the cold:

Even so, goosebumps are often a precursor to shivering — an early signal that the body needs to conserve heat.

Goosebumps on command

Some people say they can raise goosebumps simply by concentrating, without any outside trigger. The ability is very rare and has been looked at in small studies. That some people can consciously trigger a response normally considered involuntary suggests the link between the brain and the autonomic nervous system may be more flexible than we think.

In short

Goosebumps happen when a tiny muscle at the base of each hair is contracted by the sympathetic nervous system. In our furry ancestors the reflex kept them warm and helped them look intimidating; in us it lingers mostly as an evolutionary memento. Yet the same system may play a part in hair growth — and it shows just how deeply abstract experiences such as music can move us.