Why do we get goosebumps? Harvard study answers age-old mystery

CAMBRIDGE, Mass. — Goosebumps can be an odd sight. Some people get them when they’re cold, while others get them when they’re spooked or excited. So what causes these little bumps to pop up on your skin? Harvard University scientists say they have the reason and it’s all about growing hair. A recent study finds the same muscles and nerves that cause your goosebumps also tell your cells it’s time to make more hair.

Although animals with thick fur seem to use this trait to protect themselves against cold weather, it has seemed to have little use for modern-day humans. The report in the journal Cell finds muscles in the skin contract to make goosebumps. These muscles also form a bridge between sympathetic nerves and stem cells in control of your hair.

When it’s cold, your skin feels it and this system reacts. In the short-term, they’re giving you goosebumps. In the long-term however, the Harvard team says these nerves send out signals telling hair follicles to activate.

“In this study, we identify an interesting dual-component niche that not only regulates the stem cells under steady state, but also modulates stem cell behaviors according to temperature changes outside,” researcher Ya-Chieh Hsu says in a university statement.

What’s going on under the skin?

Responding to the cold, muscles (pink) in the hair follicle contract, resulting in goosebumps. The sympathetic nerve (green) releases neurotransmitters that target hair follicle stem cells (blue), also causing them to activate and grow new hair. (Credit: Yulia Shwartz, Meryem Gonzalez-Celeiro, Chih-Lung Chen, et al., Cell.)

Study authors say there are three types of tissue that make up most organs: epithelium, mesenchyme, and nerve. These sympathetic nerves that spark goosebumps are part of the body that control your responses to external stimuli, like the weather. Those nerves tie to tiny smooth muscles in the mesenchyme which connect to hair stem cells.

Using a high resolution electron microscopy, the study discovers that these nerves actually wrap around hair follicle stem cells just like a ribbon. Cold air sparks neurons to send out their signal, making muscles contract, and causing hair to stand on end.

“We could really see at an ultrastructure level how the nerve and the stem cell interact. Neurons tend to regulate excitable cells, like other neurons or muscle with synapses,” Hsu adds. “But we were surprised to find that they form similar synapse-like structures with an epithelial stem cell, which is not a very typical target for neurons.”

Scientists also find hair follicles secrete a protein which regulates the creation of smooth muscles. This then attracts the sympathetic nerve to connect, creating a full circle of skin and hair creation.

What else can your skin do?

Researchers are now exploring how the skin’s reaction to weather affects wound healing.

“We live in a constantly changing environment. Since the skin is always in contact with the outside world, it gives us a chance to study what mechanisms stem cells in our body use to integrate tissue production with changing demands,” Hsu explains.

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