Can you recall memories of blood rushing to your face when your school-teacher would suddenly call upon you to solve an equation before the whole class? Do your cheeks redden when you fall down and everyone turns to look at you? That feeling of blood rushing to our cheeks is so synonymous with public embarrassment. But why does it happen?

Blushing is understood to be universal among humans, as well as exclusive to our species. Described by Charles Darwin as “the most peculiar and most human of all expressions,” in 1872, the phenomenon of blushing is still not fully understood by scientists. In his paper titled ‘The Puzzle of Blushing,’ Professor Ray Crozier, a Fellow of the British Psychological Society, called blushing a “ubiquitous yet little-understood phenomenon” that is both involuntary and uncontrollable. “An actor might simulate a smile, laughter or a frown, but not a blush,” he said.

But, what we do know is that blushing goes hand-in-hand with embarrassment, and as such, is physiologically governed by the sympathetic nervous system, which is also responsible for our fight-or-flight response. When we’re embarrassed, our body releases adrenaline, which causes our blood vessels to dilate, in a bid to improve blood-flow and oxygen delivery. And, blood vessels in our cheeks are wider and closer to the surface, than other parts of the body — creating the reddened appearance. “As more blood flushes the face, a red complexion and the sensation of warmth develops,” Dr. Tanya Azarani, an adult psychiatrist and psychotherapist in Brooklyn, told The New York Times, explaining why blushing accompanies feelings of shame, self-consciousness, or anger.

Interestingly, “the more anxious we feel about our blushing, the more neurologically aroused we become, and the more neurologically aroused we are, the more we blush, leading to a vicious self-perpetuating cycle,” Dr. Azarani said. Basically, blushing appears to beget more blushing, especially if we try to hold it back. According to a 2009 study, if one is simply told that they are blushing, when they actually weren’t, can end up inducing it. Also, “believing that one will blush can act as a self-fulfilling prophecy,” the study notes.

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However, blushing can also be a result of feeling like one is the centre of attention. In fact, in a study where people had to sing out loud while someone stared at one side of their face, researchers found that blood-flow to the face increased only on the cheek that was being watched. However, experts also believe that shame can trigger blushing too: if a topic that makes one feel ashamed is brought up, irrespective of whether or not they are the centre of attention in that conversation, a person may blush. Also, if one feels inferior, socially or professionally, to the people around them, they can be quick to feel self-conscious, resulting in blushing.

While the utility of blushing continues to remain elusive, experts believe that blushing may have some social upsides. It is like a “built-in polygraph” — “When you blush, others know that your emotional experience is true and sincere. When people blush in an embarrassing or shameful situation, they are more likely to be seen by others as likable and trustworthy than if they had not blushed,” Dr. Marije aan het Rot, a behavioral scientist at the University of Groningen in the Netherlands, told Time. Blushing also serves as a non-verbal apology that enforces social codes. In fact, research suggests that pictures of blushing faces score higher in terms of trustworthiness. “After you do something wrong, people like you more when you blush,” says Corine Dijk, an assistant professor of psychology at the University of Amsterdam in the Netherlands, told NBC News.

Experts believe that the fact that we can’t control blushing can also make us dislike, or fear, it. Erythrophobia, or the fear of going red, is the clinical term for a fear of blushing. It is a type of anxiety disorder that can adversely affect people’s social and emotional lives. “…For a long time blushing made it really hard to meet anyone. People think it’s cute if you’re a woman, but just off-putting if you’re a man. I’m sure I’d be in a very different position in my career now if I didn’t feel I had to avoid any kind of public scrutiny. Even speaking up in small meetings makes me uncomfortable and anxious,” a frequenter of a blushing support forum, told The Atlantic. The condition can be a result of severe, or chronic, blushing. As a result, endothoracic sympathectomy, a surgical procedure that severs the nerve which triggers our blushing reflex, may be performed. In less extreme cases, cognitive behavioural therapy is also recommended.

“Most people who blush wish that they didn’t, but the blush is actually a really cool trick that your body can use to display your emotional state… What’s especially neat about the blush is that, compared to other types of emotional displays, it’s an ‘honest’ one,” Dr. Gina Grimshaw, from the School of Psychology at Victoria University of Wellington, explains. At its very core, blushing a “distinct sign of self-awareness.”