Hair removal is a multi-billion dollar industry. Now, a team of researchers at Harvard University has uncovered a piece of the puzzle of why hair keeps coming back whether you remove it with wax, thread, depilatory cream or laser. The answer, strangely, is hair-raising.

When we get goosebumps, the skin on our arms or legs gets pinched together. This action, according to the researchers, brings the sympathetic nerve cells under the skin in touch with hair follicles—long enough to activate the stem cells responsible for regenerating hair follicles and hair.

But that’s not the whole story.

New hair follicles, as they form, stimulate the formation of smooth muscle and this muscle attracts the sympathetic nerve cells to form connections with it.

Thus the cycle perpetuates itself.

The researchers, who were interested in how the stem cells of our body respond to the world around us (and not quite hair removal for aesthetic purposes), chose the stem cells of the skin for obvious reasons—since the skin is at the junction where the body meets the external world, researchers could get a closer look at how these stem cells react to external stimuli.

To get a really close look, the researchers used very high-resolution electron microscopy. “We could really see at an ultrastructure level how the nerve and the stem cell interact,” Ya-Chieh Hsu, one of the leaders of the study, told the media.

The researchers found that while goosebumps are the obvious and short-term result of exposure to the cold, prolonged exposure could signal to the body that it needs to grow more hair—in the time when humans were hunter-gatherers, body hair would have been an extra protective layer against the elements. The scientists also said that they wanted to continue looking at the effects of other environmental factors on the stem cells of the skin.

The new research, done on mice, has been published in Cell—a highly regarded peer-reviewed journal.

  1. What are epidermal stem cells?
  2. Goosebumps and how they interact with hair follicles
  3. Hair growth and temperature
  4. Takeaways

Stem cells are special cells in the body that have the ability to regenerate and regrow. In the past few decades, stem cells have been deemed an all-new horizon in the field of regenerative medicine.

They are extensively used in stem cell transplants, often done to replace cells that have been damaged considerably due to chemotherapy or introduced in the human body to help the immune system fight off many complications.

Epidermal stem cells

The epidermis or skin is constantly regenerating itself—as dead skin falls off, new cells take its place. This happens courtesy of the stem cells present in the skin—they have the capacity to differentiate into multiple skin cells. Apart from playing a central role in wound repair, epidermal stem cells are pivotal to maintain body homeostasis.

Epidermal stem cells are active during skin renewal that takes place after an injury and throughout life. These cells are distributed in the basal layer of the epidermis—the layer where new skin cells are made and then pushed up towards the surface as dead skin cells are shed. The hair follicles are in the second layer of the skin—dermis—under the surface.

New research shows that when we get goosebumps, the skin of our arm or leg gets pinched together and this activates these stem cells.

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Whenever we’re in fear or step into a chilled room, the hair on our skin stands, giving us goosebumps. This is because of the sympathetic nervous system, which is responsible for invoking fear and fight or flight responses. When we are afraid or feeling cold, tiny muscles present on the skin contract, making body hair erect for a short period.

However, it was a brand new discovery when researchers in Harvard examining the skin under extremely high resolution found that the sympathetic nerves not only associated with the muscle but also formed a direct connection to the hair follicle stem cells by wrapping around the cells.

Another thing that the researchers confirmed was that the nerve indeed targeted the stem cells. Under prolonged exposure to the cold, the nerve was activated at a much higher level and more neurotransmitters were released, causing the stem cells to activate quickly, regenerate the hair follicle, and grow new hair.

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Hair follicles indeed react quickly in cold temperatures. Goosebumps are important for regulating the stem cells that regenerate hair.

In the skin, the muscle that contracts to create goosebumps is necessary to bridge the sympathetic nerve's connection to the hair follicles.

This is just one study on how our sympathetic nervous system responds to the world around us; the researchers at Harvard said they planned to look into this further.

Of course, the idea that goosebumps foster hair growth all over the body also needs to be studied in greater depth. That said, the Harvard researchers were able to see the nerves "wrapping" around the hair follicles when the animal models (mice in the lab) were exposed to cold temperatures: an exciting discovery to a question raised by the father of evolution Charles Darwin himself—why do we get goosebumps?


  1. Lau J. Getting to the bottom of goosebumps. The Harvard Gazette, 20 July 2020.
  2. Shwartz Y., Gonzalez-Celeiro M., Chen Chih-Lung, Yu-Hua Tseng, Sung-Jan Lin and Ya-Chieh Hsu et al. Cell types promoting goosebumps form a niche to regulate hair follicle stem cells. Cell, 16 July 2020.
  3. Senoo M. Epidermal stem cells in homeostasis and wound repair of the skin. Advances in Wound Care (New Rochelle). July 2013; 2(6): 273-282. PMID: 24527349.
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