Why do we get goosebumps?

Goosebumps happen when tiny muscles at the base of each hair follicle contract and pull the hair upright. The reaction is involuntary and is driven by the sympathetic nervous system, the same system that runs the fight-or-flight response. Cold, fear and a startling stimulus are the classic triggers. The reflex is generally understood as a remnant from ancestors with thicker body hair, and it does little for humans today. [1] [2] [3]

According to [livescience.com](https://www.livescience.com/32349-what-causes-goose-bumps.html), thousands of tiny muscles called arrector pili lie below the skin, one for each hair. Nerves coiled around them send electrical signals that tell the muscles to contract. The muscles raise their attached hairs, and the skin around each hair puckers into a bump. The name comes from the textured skin of a plucked goose. The technical term is piloerection. [4] [1]

In animals with thick fur, raised hair traps a layer of air that insulates the body. When an animal feels threatened, the fluffed coat also makes it look larger. The [health.harvard.edu](https://www.health.harvard.edu/blog/wondering-about-goosebumps-of-course-you-are-2020080320688) article gives the porcupine's quills as a dramatic example, and suggests this link to threat may explain why the sympathetic nervous system controls the reflex. [livescience.com](https://www.livescience.com/32349-what-causes-goose-bumps.html) reports that piloerection occurs in nearly all mammals and in many birds and reptiles, so scientists believe the trait was present in the earliest mammal. [2] [4]

For humans the benefit is unclear. Harvard Health lists possible heat-saving effects: muscle contraction generates a little heat, pores close, and standing hairs trap air. It adds that each may matter more for furry animals, and that people who could not form goosebumps would not necessarily have trouble controlling temperature. Amy Paller of Northwestern University is quoted in Live Science saying that for humans it really does not do anything to protect us. Cleveland Clinic, by contrast, describes the response as helping conserve heat. [2] [4] [5]

A 2020 study in Cell, led by Ya-Chieh Hsu and Sung-Jan Lin, examined mouse skin. Reported by the [nih.gov](https://www.nih.gov/news-events/nih-research-matters/what-goosebumps-are) summary, it found that the sympathetic nerves connect to hair follicle stem cells through the arrector pili muscle. When the researchers destroyed the muscle, the nerve-stem cell connection was lost and new hair growth was delayed. Mice exposed to cold produced new hairs in under two weeks. The researchers proposed a two-layer response: goosebumps give quick short-term relief, and prolonged cold prompts the stem cells to regenerate the hair coat. The work was done in mice, and Harvard Health notes the idea applies most clearly to animals with fur. [6] [2]

The sympathetic nervous system receives input from many brain regions, including those involved in motivation, arousal and emotion. Harvard Health says this is why moving music or art, awe, pride, excitement and fear can all produce goosebumps. Cleveland Clinic adds anger, shock, intimacy and sexual arousal, and describes frisson, or psychogenic shivers, in response to music, movies, ASMR or an empowering speech. [2] [5]