Dear Nolan,

If you’ve ever been outside on a cold day, you may have noticed how your arm hairs stood up and you felt some goosebumps.

Humans get goosebumps for different reasons and one of those reasons has to do with temperature.

My friend Ryan Driskell, an assistant professor at Washington State University, is really curious about the innerworkings of skin.

Ryan Driskell, scientist
Ryan Driskell

Driskell said that all of the hair on your arms grows out of little hair follicles in your skin. At the bottom of the follicle is a little hair factory that makes your hair. It’s also attached to a tiny, little smooth muscle called an arrector pili.

When we get cold, sometimes that little muscle contracts, or pulls on the hair follicle, to make the hair on your arms stand up.

“But it’s not just standing up straight,” Driskell said. “A lot of the time the hair is set to an angle.”

Though the hairs might be small, together they are able to create a kind of micro-environment for your body.

The hairs that are tilted at an angle help trap the air close to the body, which can help you to warm up, Driskell said.

That’s just one of the reasons we get goosebumps. Perhaps you’ve experienced goosebumps in other situations. If you are like me, maybe your hair stands on its end when you sense some kind of danger.

Dr. Universe cartoon cat character looking up to the skyMaybe you’ve seen a cat puff up really big when it walked past a dog. This helped the cat look bigger and stronger than if it was just showing off its normal hair. Cats have a lot more hair follicles than humans. That also means they have a lot more hair that can stand up on end.

While humans might not be as hairy as a cats or a dogs, they do sometimes respond in a similar way when they sense a threat. Animals have a fight or flight response, which means they can run away or face their fears head on.

Millions of years ago, your human ancestors were much more hairy than humans are today. Goosebumps may be a kind of leftover reflex from the days when your more hairy ancestors were experiencing that kind of fight or flight response.

Driskell also told me you are actually born with all the arrector pilis and hair follicles you will ever have. When you get a scar, the hair and erector pili don’t grow back.

In the Driskell Lab (, scientists are working to find out how to regenerate the damaged arrector pilis and hair follicles so that the body can fully heal itself—including getting back to making goosebumps.

While goosebumps are something almost everyone feels at some point, we may experience them at different times and for different reasons. Maybe one day you can do some research to help us discover more about the biology and psychology that’s going on behind our goosebumps.

Dr. Universe

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