Blush to judgment

Why do humans alone turn red in the face?

(Cristina Byvik / Union-Tribune photo-illustration)
(Cristina Byvik / Union-Tribune photo-illustration)
Frans de Waal, an Emory University primatologist, says of blushing, “It seems not to be to our advantage to do it, to involuntarily reveal our inner emotions.” (Catherine Marin)
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Blushing is a temporary reddening of the skin (erythema) caused by rapid dilation or widening of underlying blood vessels, especially in the face, neck and upper chest.

It's involuntary and universal in humans, usually the result of an emotional response. Flushing – a cousin to blushing – is different: It tends to be more physically intense. It covers more of the body. And it seldom has a mental source.

Excessive blushing is the principal symptom of social anxiety disorder, a condition that affects 7 percent to 13 percent of people at some point in their lives. A fear of blushing is called erythrophobia.

Online: Read earlier articles in our series on Darwin's legacy at darwin2009

After explaining the origin of species and the descent of man, Charles Darwin – the 19th-century English naturalist-turned-icon – shifted his attention to something really inexplicable: blushing.

It was, he said, “the most peculiar and the most human of all expressions.”

No other species blushes. We do so involuntarily, usually from shame, guilt or embarrassment. People of every race blush, but not people of every age. The very young and very old seem to blush little or not at all. But blind people blush. And women blush more than men.

These observations are well-documented, as obvious as our reddened faces, but they remain not much better understood than when Darwin penned his 1872 classic “The Expression of the Emotions in Man and Animals,” which remains in print today.

“It's one of evolution's great mysteries, I think,” said Frans de Waal, a professor of psychology and primate behavior at Emory University in Atlanta.

“What is the evolutionary value of blushing? It seems not to be to our advantage to do it, to involuntarily reveal our inner emotions. If we're trying to manipulate or lie, actions in furtherance of individual goals as opposed to the goals of others, blushing would not seem to be helpful. And yet everyone blushes, except the psychopath.”

Over the years, many reasons have been suggested.

“Some psychologists argue that the blush is an expression or bodily display of embarrassment; some argue that it is an expression of shame, guilt or shyness,” said Ray Crozier, a professor of psychology at the University of East Anglia in Norwich, England, and author of multiple papers on blushing.

“I have suggested that we blush when there is the risk of something being revealed that is pertinent to our self and that we would not want others to know about.”

The most common hypothesis posits that blushing is an evolutionary adaptation that benefits both individuals and the larger social group.

“The only way to explain blushing is to look at it as a signal of honesty,” said de Waal. “People want to work with somebody who feels shame, who worries about the perceptions of others. Dishonesty is something we don't like in others.”

In other words, he said, blushing likely moderates bad behavior. And it is a public signal of remorse. If a miscreant blushes with shame or embarrassment, experts say, that is a public admission of wrongdoing and a nonverbal request for forgiveness. Blushing can diffuse tense situations, perhaps reducing the chance of violence, which benefits neither individual nor group. Blushing helps people – and societies – get along.

“The problem with the standard explanation is that people often blush when they have done nothing whatsoever to create problems in the group,” said Mark Leary, director of the social psychology program at Duke University.

“For example, people sometimes blush when complimented, singled out for positive attention, having 'Happy Birthday' sung to them, or merely stared at. My own theory, which I published in the 1990s, suggests that blushing arises from undesired social attention.”

That undesired attention can be negative, such as embarrassment or criticism, or positive, such as lavish praise or excessive visual admiration, or being serenaded when one does not know how to respond, said Leary.

“Blushing seems to signal, 'I'm uncomfortable with the amount of social attention I'm receiving' and actually deter others' attention. People find it hard to continue to look at other people who are blushing.”

But what if the act of blushing isn't apparent? Dark-skinned people blush. What's the benefit of a signal unseen?

“We have two possibilities,” said Christopher Boehm, an anthropologist at the University of Southern California. The first is that blushing is simply an irrelevant physical phenomenon that persists because, while it provides no real value, it doesn't cause harm, either. It's just there – like our appendix.

The second possibility, according to Boehm, is that blushing originated as an internal physiological cue. “The original adaptive function was likely to have been that the burning sensation reminded someone sharply that a deviant act had occurred, which in turn served to inhibit future such acts and reduced the potential reproductive damage society's punitive reactions can bring about.

“If the original population was very dark skinned, this signal would have been private. If it wasn't, it would have been public. In either event, the signal would have assisted people in controlling their deviant tendencies in ways that ultimately were individually adaptive. The advantage of this hypothesis is that it works regardless of skin color and regardless of whether blushing is visible in people with dark skins.”

Red all over

No less confounding is why women appear to blush more easily than men. One notion suggests it's simply a primitive physical cue intended to draw and hold the attention of prospective mates. It's a sign of excitement and arousal.

Darwin and his contemporaries thought so. Blushing was deemed lovely and virtuous. The English novelist Jane Austen (1775-1817) considered it to be an appealing sign of feminine modesty and sincerity. The French Impressionist painter Pierre-Auguste Renoir (1841-1919) favored blushing beauties.

More recently, a Scottish study noted that people find pinker faces to be more appealing than those that are pale or tinged with other colors. Pink, concluded scientists at the University of St. Andrews, suggests health and greater reproductive ability.

But Leary at Duke University said it's much more complicated than that.

“There are many things going on here,” he said. “On one hand, it's possible that women's greater social orientation makes them more sensitive to others' attention and judgment. Or perhaps they feel more vulnerable when they are the focus of attention.

“But I also think that women are less likely to hide their embarrassment than men. And given current styles of clothing in the United States, women's blushes are easier to see because blushes often start on the upper chest and neck before moving to the face.”

Humans alone blush, say experts, because doing so demands significant self-awareness and cognitive development. De Waal, who has studied animal behavior for years, says a pet dog who has just destroyed the garden may roll onto its back, belly exposed in obvious submission, but that's not an expression of guilt.

“It's anticipation of punishment. The dog knows he's in trouble.”

Similarly, Crozier at the University of East Anglia said very young children don't blush until they have developed sufficient cognitive skills and social awareness, usually around 3 or 4 years of age. Teenagers and 20-somethings, who tend to be entirely too self-aware, are often full-fledged blushers.

High intelligence is not a requirement of blushing, said Leary at Duke.

“Many species react to being stared at by performing other behaviors that often accompany human blushing,” he said. “For example, downcast eyes and a silly smile are also part of other primates' signs of social discomfort or deference, so blushing may be an add-on to an earlier (response) system.”

Darwin believed blushing was an inherited trait, though not the result of natural selection. “By frequent reiteration during numberless generations,” he wrote, “the process will have become so habitual, in association with the belief that others are thinking of us, that even a suspicion of their depreciation suffices to relax the capillaries, without any conscious thought about our faces.”

Modern scientists say Darwin got it basically right. A person's propensity to blush probably does have a genetic component, just as personality traits like shyness and fearfulness do.

But that doesn't mean problematic blushing can't be controlled. There is a surgical procedure called endothoracic sympathectomy, which involves snipping nerves in the spine that govern blushing and sweating. But the procedure has serious side effects and is considered an act of last resort.

More typically, excessive blushing is treated with nonmedical methods like biofeedback, in which people attempt to consciously control autonomous body functions like heart rate, sweating and skin temperature.

Crozier said it's also possible simply to desensitize oneself to causes of blushing. “If my ideas on blushing are correct, the blush is elicited by particular circumstances and is not an automatic response to particular incidents,” he said. “Its occurrence will depend on the individual's interpretation of the situation.”

Leary agreed: “People consciously override evolutionary adaptations all the time. When a person resists eating something desirable, uses birth control, helps an enemy or works hard not to flinch during a painful medical procedure, they are resisting evolved tendencies.”

But it may be impossible, Leary said, to flush the blush entirely.

“My hunch is there are very few people who could not be induced to blush under certain circumstances. True, some people blush more than others, and some people learn tactics to control their blushing, but few people are genuinely blush-free.”