Many mammals exhibit an automatic physiological response known as “piloerection,” which involves the hair standing on end. Humans exhibit this response, too, but since our hair is sparse, it manifests mostly as goose bumps. Image by Geran de Klerk via Unsplash.

The puzzle of piloerection

Do you remember the last time you got goose bumps? Not the kind you get when you’re cold — those aren’t particularly memorable. I mean the other kind — the ones that start from within, that come with a surge of feeling, the ones sometimes called “psychogenic.”

I last got them a couple weeks ago while I was reading a novel — The Heart’s Invisible Furies, by John Boyne. There’s a scene toward the end that really got me — there’s a revelation, let’s just say. It kicked off a chilly, tingly wave that started at the back of my neck. The experience was intense enough that, as I was writing this, thinking back on that scene, I got them again.

Vladimir Nabokov once observed that a novel is not judged by the heart or the brain but by the spine. “It is there that occurs the tell-tale tingle,” he wrote. He had a point: tingles tell a visceral kind of truth.

Surely I’ve gotten goose bumps thousands of times, but, for whatever reason, that was the episode that moved me to look into them. It turns out that goose bumps — a universal part of human experience for probably millions of years — have just recently become a phenomenon of intense scientific interest. Fittingly, this interest seems to have come on suddenly, in one subfield, and then spread. But despite all this recent attention, goose bumps remain a puzzle. And something of a hairy one.

Before we get to the puzzle, some preliminaries. Goose bumps go by different names. In the US they were, until quite recently, often known as “goose flesh.” You might also see them called “goose-tingles” or “goose-pimples.” Terms for them in many languages reference the skin of barnyard birds. A more literary word for goose bumps is “horripilation,” a reference to the fact that they come on in moments of horror; a more scientific word is the staid-sounding “piloerection.”

Goose bumps brought on by a cold breeze. Image by Everjean via Flickr (CC BY-SA 2.0).

Goose bumps actually result from a frenzy of muscular contraction. Attached to the base of each hair follicle is a bit of muscle. When those muscles — the arrector pili — contract, the follicle is raised and the skin gets that pimply look. These are smooth muscles, the type you can’t control voluntarily — the same type of muscle you find in your gut, lungs, and other internal organs.

The bumps themselves are just an outward manifestation of an inner experience that also goes by a bunch of names — chills, thrills, tingles, shivers, shudders, tickles. You can experience this inner part without the outer part, but often the two go together, and the terms are all used somewhat interchangeably.

Whatever you call them, goose bumps are a textbook example of a vestigial physiological response: they evolved for a purpose they no longer serve. One of their original functions was thermoregulation. If you’re covered in fur or feathers, making those tiny appendages stand on end aids insulation by creating a layer of motionless air near the skin. Piloerection also makes you look bigger, which is useful if you’re trying to appear threatening. But given our modern furlessness, a wave of goosebumps doesn’t really regulate our temperatures. Nor is it much good for intimidating our rivals.

Charles Darwin, you may not be surprised to hear, was fascinated by piloerection. In his 1872 book, The Expression of the Emotions in Man and Animals, he observed that “hardly any expressive movement is so general as the involuntary erection of the hairs, feathers and other dermal appendages.”

A figure from Darwin’s ‘Expression’ showing a dog with hackles bristling. In this case piloerection would serve to make animal look bigger and thus more intimidating. Image: public domain.

He was perhaps most interested in piloerection as brought on by fear. He described how the phenomenon manifests in dogs and baboons, peccaries and parrots. Ever the experimentalist, he once brought a stuffed snake into the monkey-house at a zoo to see how the animals would react. He took special note of the spot-nosed monkeys whose tails bristled up visibly.

A cat with its hair bristling up in fear at the sight of a dog. Image by Peretz Partensky via Flickr (CC BY-SA 2.0).

In humans, fear and cold are not the only type of experience that sets our hairs on end. And things get more puzzling when we look at the fuller range. Goose bumps can be brought on by the screech of nails on a chalkboard or, according to some, by the experience of awe. The devout sometimes get them at moments of religious intensity; mathematicians may get them when faced with an elegant proof.

A wave of recent empirical work on goose bumps has looked especially closely at their role aesthetic responses—responses like the one I had to the John Boyne novel, responses like the one that Nabokov mentioned.

The first study in this vein on this was done in 1980 by Avram Goldstein, then of Stanford University. Focusing on the internal sensation, he referred to the phenomenon as “thrills.” The paper was primarily a reconnaissance mission, a first pass. He had people describe what “thrills” felt like and when they tended to occur.

Only about half of people reported ever having them. (The other half were skeptical they were a real phenomenon.) Those that did most often described these “thrills” as originating at the spine or neck and then radiating out from there — to the face, scalp, arms, and beyond. More intense episodes tended to spread farther and last longer.

The subjects reported that thrill episodes occurred in a wide variety of contexts — such as when watching emotional interactions between people (67% of subjects); when suddenly figuring out a problem (57%); when smelling certain fragrances (39%). But the most commonly reported context — mentioned by 96% of people who experienced thrills — was listening to music.

Darwin himself once described music-induced chills. In his autobiography he wrote that he would time his walks “so as to hear on weekdays the anthem in King’s College Chapel. This gave me intense pleasure, so that my backbone would sometimes shiver.”

Goldstein’s observations about music kicked off a flurry of further work. One influential follow-up study was conducted by the Estonian neuroscientist Jaak Panskepp. He was curious about the kinds of music that brought on chills. What he found was that people were more likely to experience chills in response to sad songs than to happy songs. The most chill-inducing songs, he observed, dealt with themes of “bittersweet sadness” and “lost love.” In later work, Panskepp reported that patriotic songs also do the trick. For American subjects, he noted, the ‘Battle Hymn of the Republic’ really sets the forearm flesh prickling.

Goosebumps and chills are also associated with patriotic music and displays. Image by Stephanie McCabe via Unsplash.

Since these pioneering early studies, a subfield has sprung up around these “aesthetic chills,” as they’re now commonly known. Researchers have developed fancier, more objective methods for measuring them, and they’ve started to explore aesthetic chills in response to other forms of art.

A recent study, for instance, looked at film. The researchers found that cinema-induced goose bumps tend to occur in response to “displays of prosocial behavior.” The paper also reported that goosebumps sometimes co-occurred with crying — a confluence the authors dubbed “goosetears.” Another study looked at poetry. The researchers found that chills tend to turn up at the ends of lines or stanzas, or sometimes at the end of the poem as a whole. In each art form, there seem to be certain features that bring out the bumps.

Through these studies we’re starting to get a handle on when people get chills. Another key question is who gets them. Again, according that original study by Goldstein, aesthetic chills are unfamiliar to about half of us. This variability, it turns out, is hardly random — it’s linked to a personality dimension known as “openness to experience.”

“Openness to experience” is part of the so-called “Big Five” — the five dimensions that together are thought to characterize variation in personality across individuals. Openness concerns how much we seek out and notice, how much we like to engage intellectually and imaginatively. Like the rest of the Big Five, it’s assessed with carefully crafted, meticulously validated surveys.

If you were to take one such survey — the revised NEO personality inventory — you would eventually come to Item 188, which reads:

“Sometimes when I am reading poetry or looking at a work of art, I feel a chill or wave of excitement.”

Of all the questions in this survey that try to gauge openness, this one — item 188 — turns out to be one of the best. And not just in the US, or among English speakers. A 2007 study by Robert McCrae reported that Item 188 is significantly correlated with total “openness to experience” in 50 of 51 cultures in which it was tested. Combining all groups, item 188 is the single best indicator of overall openness, in fact. These findings led McCrae to title his report “Aesthetic chills as a universal marker of openness to experience.”

One thing you might be wondering, as I was: Are all psychogenic chills “aesthetic chills”? Not necessarily. There’s a newer wave of work examining goose bumps and chills as a common response to what we think of as “moving experiences.” The psychological anthropologist Alan Page Fiske and colleagues have started to investigate these experiences under the banner of the phrase kama muta — Sanskrit for “moved by love.” The feeling of kama muta comes about, according to Fiske and colleagues, when we experience a “sudden intensification of communal relations.” It’s a fundamentally social emotion. It wells up when we watch people reunited after a long absence, when we witness acts of heroism or patriotic displays.

So we’ve got a handle on what chills are, on when they tend to occur, and on who tends to get them. Now on to those puzzles.

First there’s the question of why chills so often start at the back of the neck. Then there’s the question of whether chills and goose bumps are two sides of a coin — inner and outer — or are brought on by subtly different experiences. There’s also the question of why chills and “openness to experience” are so tightly linked.

But perhaps the hairiest puzzle raised by goose bumps is this: What unites the experiences that seem to bring them on? Why might bittersweet sadness lead to the same physiological response as horror? What does poetry have to do with thermoregulation? Why would our body link heart-warming social experiences with cringe-inducing sounds?

Attempts to explain why we get goose bumps have usually been piecemeal, applying only to a narrow range of contexts. Perhaps the closest thing we have to a unifying hypothesis is the one put forward by Jaak Panskepp. His idea was that bittersweet music brings on chills because it resembles the distress calls primates make when they become separated. In a 2002 paper he and a co-author wrote: “This may be one of nature’s ways to promote reunion; the experience of separation may evoke thermoregulatory discomfort which can be alleviated by the social ‘warmth’ of coming together again.”

Maybe there’s a more general idea to be developed here — one that bridges aesthetic chills and kama muta type chills. Darwin’s music-induced chills, if you recall, were in response to an anthem — a song designed to stir fellow-feeling. And that scene in the John Boyne novel that set me tingling? It described a long-deferred reunion. A lot of psychogenic chills could be our body urging us to connect, to come out of the social cold.

This is not a particularly satisfying account, I’ll admit. But I’m guessing other, better accounts are not far so off. Goose bumps present a puzzle that’s simply hard to resist. They’re an unwilled, evolutionarily ancient, predictable response to certain external stimuli. Yet they also come about at moments of intense togetherness, of intellectual insight, of aesthetic rapture. They’re part of a heritage we share with many other animals, but also deeply human.

I’ll confess that part of me doesn’t want to unweave this rainbow. Part of me is happy to just let this mystery lie, to have it sometimes catch me off guard, at the back of the neck, with a tingly reminder that there are things about us — about our minds, about our bodies, about human experience — that we just don’t yet fully understand.

Note: This post originally appeared in audio format on the ‘Many Minds’ podcast (@ManyMindsPod). You can listen to the episode here.

Our world is brimming with beings—human, animal, and artificial. We explore how they think, sense, feel, and learn. A project of @DivIntelligence & @kensycoop.