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What are goosebumps and why do we get them? The evolutionary explanation of piloerection

All it takes is a breath of wind Freddo to find ourselves with skin covered in small dots: the goosebumpsin technical jargon piloerectionan involuntary defense mechanism (like shivering) activated when we are cold, afraid, or experience very intense emotions. From a physiological point of view, goosebumps occur when i muscles hair erectors yes they contractpulling up the hair and causing the classic rough appearance of goosebumps. Even the fear it activates the same mechanism and, through the “fight or flight” response, makes the animals’ hair stand on end when they are faced with danger: the standing hair makes them appear larger and more frightening. Sometimes we experience goosebumps for no apparent reason, for example when we feel great pleasure, strong amazement or intense excitement. Let’s see what others functions could it have and what is triggering it.

Goosebumps are a defense mechanism: what it is and what happens to the body

Goosebumps – more technically piloerection or cutis anserina – is the involuntary formation of “hills” on our skin, which make it rough. It is a temporary mechanism that allows us to defend ourselves from the cold and respond to any threats through the action of the muscles responsible for erecting hair.

Our body perceives the cold, and temperature variations in general, through special thermal receptors present throughout the body. When it is cold, thermoreceptors send signals to the brain, specifically to the thermoregulation center located in the brain.hypothalamusto communicate this drop in temperature and activate the thermoregulation systems.

Through the sympathetic nervous system, the brain releases norepinephrine which signals the hair arrector muscles to contract, literally pulling the hair into an erect position: in doing so the skin curls and forms the typical “hills” of goosebumps. This mechanism allows a thin layer of air to be trapped between the hairs which works as a insulating pad which protects from the cold.

This same system is also activated by fear. When animals are faced with danger, the autonomic nervous system activates “fight or flight” reactions, causing the arrector pili muscles to contract, and with the fur standing on end the animal may appear larger and more fearful to ward off the threat. .

scared cat

Why we get goosebumps: the evolutionary meaning

Our hair is too thin and small to protect us from the cold, and for several thousand years now we have no longer needed to grow fur to scare away predators. But if until recently the role of piloerection was not clear and it was thought to be just a relic of our primate past, recent research conducted by a group of Harvard researchers is highlighting its unexpected function, at least in guinea pigs.

The answer lies in the structure of the hair bulb itself, and concerns the three groups of cells responsible for piloerection: the erector muscle of the hair, the nerve endings of the sympathetic system and the hair stem cells. The researchers interrupted the communication between them in various ways: first by eliminating the sympathetic neuron, then the norepinephrine receptors on the hair stem cells, and finally the erector muscle. The result did not change: the hair grew much more slowly or not at all, a sign that these groups of cells may also play a role in hair growthwith the erector muscle acting as a bridge between the neuron and stem cells.

The hypothesis is therefore that the “it’s cold” signal triggers an immediate response (goosebumps) to increase the temperature, but also a long-term response by stimulating the stem cells to produce new hair and thicken the fur to facing the cold. This research, if confirmed in humans, would open the way to new possibilities on hair regrowth.

piloerection

Because we get goosebumps even when we feel strong emotions

We also get goosebumps in response to very strong emotional stimuli such as amazement or excitement, but the reason why this happens is still a mystery to be solved.

One of the possible explanations that have been proposed is called peak arousal hypothesis and claims that emotional piloerection is activated when a peak of the emotion felt, positive or negative, is reached. According to the theory of vigilancefor our brain there are no “positive surprises”, but every unexpected novelty can represent a danger. Thus, an unexpected note, an increase in volume or a change in the melody of a song alerts us, causing goosebumps. Then the rational part of the brain “explains” to us that we are safe and makes us perceive those goosebumps as a positive sensation.

Although these theories offer plausible explanations, it still remains to be clarified why, even if we know them by heart and know what awaits us, a memory, a song or a film heard and seen dozens of times is always able to trigger the same reaction of amazement, wonder… and goosebumps.

The reality is that it is difficult to study the emotional basis of goosebumps on people, whose response is highly subjective and linked to one’s own experiences and sensitivities. It is certainly a very fascinating and interesting topic for research, but until we have more detailed data and information, we can only continue to enjoy goosebumps every time we listen to our favorite song.

Sources

Shwartz, Y., Gonzalez-Celeiro, M., Chen, C.L., Pasolli, H.A., Sheu, S.H., Fan, S.M., Shamsi, F., Assaad, S., Lin, E.T., Zhang, B., Tsai, P.C. , He, M., Tseng, Y. H., Lin, S. J., & Hsu, Y. C. (2020). Cell Types Promoting Goosebumps Form a Niche to Regulate Hair Follicle Stem Cells. Cell, 182(3), 578–593.e19. Schoeller, F., Jain, A., Pizzagalli, D.A., et al. The neurobiology of aesthetic chills: How bodily sensations shape emotional experiences. Cogn Affect Behav Neurosci 24, 617–630 (2024) McPhetres, J., & Zickfeld, J. H. (2022). The physiological study of emotional piloerection: A systematic review and guide for future research. International journal of psychophysiology : official journal of the International Organization of Psychophysiology, 179, 6–20. Jain, A., Schoeller, F., Horowitz, A., Hu, X., Yan, G., Salomon, R., & Maes, P. (2023). Aesthetic chills cause an emotional drift in valence and arousal. Frontiers in neuroscience, 16, 1013117. McPhetres, J., Gao, H. H., Kemp, N., & Khati, B. (2024). Piloerection persists throughout repeated exposure to emotional stimuli. PloS one, 19(9), e0309347.