"Blushing is the most peculiar and most human of all expressions," Charles Darwin once wrote, and he wasn't wrong. Though certain species of bird pinken up as a means of communication, and uakari monkeys have red faces when in good health, we seem to be the only animal that flushes as a sign of embarrassment.
"It's a very truthful signal," says Prof Sophie Scott, the director of the Institute for Cognitive Neuroscience at University College London. "It's not fakeable, and there aren't many things that humans do that fall into that category. You can't blush on command."
Blushing is caused by your sympathetic nervous system – the same one that kicks in when you're stressed or frightened – triggering your fight-or-flight response. Your brain releases adrenaline, which widens the blood vessels in your face (known as vasodilation), increasing blood flow to the skin and producing a visible shift in colour.
"Everybody blushes," says Scott. "When it happens, your skin gets hotter, too. So there's this hall of mirrors effect: you know you're blushing, other people know you're blushing, and they know you know you're blushing." Which, of course, can make you blush even more. Other animals might exhibit involuntary physical reactions such as laughing, but blushing seems to be unique to us because it's linked to our theory of mind: our ability to guess what other people are thinking.
This is important because we're social animals: cooperation is what allowed us to survive and thrive in our earliest days. In early human societies, committing a faux pas, making a mistake or challenging a leader might have led to open conflict or expulsion from the group. It's likely that blushing emerged as a way to signal recognition of rule-breaking, or genuine remorse: a way to calm a tense situation down before it escalated.
"It seems to be associated with increased trustworthiness," says Scott. "When somebody blushes easily, you're more likely to know if they're lying to you, for instance – or even if you don't, you think that you can. That bonding and closeness is also what helps us work in groups. We're apex predators because we can work cooperatively and, usually, read each other's intentions really clearly."
Obviously, blushing can still be useful today for all of the reasons above. If we've dropped a clanger at work, it can be helpful to have an unfakeable signal that we genuinely regret it. But if we're prone to blushing and hate it, is there anything we can do?
The short answer is very little. But it also might not be the disaster you think. Frequent blushers seem to view blushing more negatively than people who don't blush all that much: if you're aware that you blush a lot, it can create feelings of shame or self-awareness. If you're an infrequent blusher, on the other hand – or you don't tend to notice when you do it – then you might associate it with getting an unexpected compliment or being publicly recognised for an achievement.
The good news is that, whatever it feels like, you might not actually be blushing much more than anyone else. "Our research indicated that when embarrassed, people who weren't frightened of blushing blushed as much as people who were frightened of blushing – they just didn't notice it so much," says Prof Peter Drummond, the lead author on a study examining the gap between actual and perceived blushing. "When we brought this to their attention, they started to become more concerned about blushing. In this way, being worried that you might blush could actually trigger it in certain situations. However, it's comforting to know that most people don't even notice that others are blushing during social interactions because their attention is focused on speaking or thinking about what to say."
"Given that being worried about blushing can become a self-fulfilling prophecy, reducing that anxiety can reduce how often we blush," says Drummond.
Finally, it's worth considering that, even if you hate it when you blush, there's a decent chance that it's doing you good overall. "I think of blushing as a 'letting off steam' response, as it shares the same physiological mechanism as flushing during exercise," says Drummond. "Although we might feel hot and bothered when we blush, we generally feel better once we cool down. In fact, blushing might help dissipate unpleasant emotions such as anger, embarrassment and shame, just like flushing helps to dissipate heat generated during exercise."
In other words, it's showing other people you're sincere while also helping to calm you down. Nothing at all to be ashamed of.