Why We Get Goosebumps?

Our body trembles when it feels cold, which is beneficial in the evolutionary process: uncontrolled shaking can encourage muscles to produce heat. But, have you ever thought about why we get goosebumps?

The latest research provides an answer: Regulating stem cells to control the growth of hair follicles and hair!

In animal experiments, scientists found that when goose bumps occur, the contraction of certain muscles is related to the sympathetic nervous system. When cold is felt, these muscles bridge the gap between sympathetic nerves and hair follicles.

In the short term, it will make hairs stand upright. In the long run, it seems to promote hair growth. Researchers say this is an important link between stem cells and external stimuli from the body.

Ya-Chieh Hsu, a biologist from Harvard University, said: “The skin is a fascinating system. There are multiple stem cells surrounded by many different types of cells, and they are located on the interface between the body and the outside world. Therefore, its stem cells may respond to various stimuli. In this study, we found an interesting dual-component niche that can not only regulate stem cells in a steady state, but also modulate stem cells behaviors according to temperature changes outside."

The team of researchers used high-resolution electron microscopy to identify this hair-growth regulation system, which involves the three types of tissue found in many organs: nerves (the sympathetic nerve), mesenchyme (holding the small muscles), and epithelium (the hair follicle stem cells).

Although the connection between nerve and muscle was already known in this specific system, the link to the hair-regulating stem cells is a new discovery, and an unusual one - here, those synapse-like connections are made to stem cells instead, wrapping around them like ribbons.

The research also showed how prolonged cold puts the sympathetic nerves in a state of high alert, exceeded the normal low-level activation that they spend most of their time at. More neurotransmitters are released, triggering quicker activation of the stem cells and, ultimately, quicker hair growth.

Most importantly, the team of researchers established that the muscle was indeed an essential link between nerves and follicle stem cells – when the muscle was removed, the connection was lost. Anyway, according to the activity observed in mice, the growth of the muscles is actually triggered by the hair follicles themselves.

Biologist Yulia Shwartz says, "We discovered that the signal comes from the developing hair follicle itself. It secretes a protein that regulates the formation of the smooth muscle, which then attracts the sympathetic nerve. Then, in the adult, the interaction turns around, with the nerve and muscle together regulating the hair follicle stem cells to regenerate the new hair follicle.”

While these same interactions haven't been observed in humans yet, biological similarities between mice and other mammals in this area make it likely that the same processes are going on underneath our own skin.

The research has been published in Cell.