Whether we realise it or not, most of us have a knee-jerk reaction when we see someone with a facial disfigurement, such as psoriasis, a cleft lip, or a birthmark.
We may sit away from them on the bus, hesitate to shake their hand, or even give a barely masked look of revulsion.
A new study suggests these disgust reactions stem from an ancient disease-avoidance system that normally prevents us from catching illnesses. Essentially, we treat facial disfigurements like infectious diseases.
Psychologists have recently begun to uncover where disgust comes from, with some researchers believing the emotion is similar to fear.
"Fear evolved to keep you away from large animals that want to eat you from the outside," says Valerie Curtis, a behavioral scientist at the London School of Hygiene and Tropical Medicine, who wasn't involved in the study.
"Disgust evolved to keep you away from smaller animals that kill you from the inside."
Our subconscious minds constantly scan the environment for signs of potential diseases, she says.
If we see one, disgust kicks in and we avoid that object or person like the plague.
But it seems our disease-avoidance system sometimes gets it wrong.
Previous studies suggested these mistakes underlie the aversion people have to various disfigurements.
For this to be true, our responses to people with facial disfigurements, which aren't contagious, would have to be the same as our responses to people with infectious diseases.
To test this idea, psychologists at Macquarie University in Sydney, Australia, had 98 participants watch three videos of a person interacting with an object.
Each featured a different actor—one who looked healthy, one who had a port-wine stain birthmark, and one who had flu-like symptoms.
The clip ended with the model putting a prop—a snorkel, towel, or harmonica—in his mouth. The participants then had to imitate the actors, whom they believed had just used their props.
Researchers recorded how far the participants were willing to go with their imitations and how often they made disgusted faces or exhibited disgust-related behaviours, such as wiping the prop.
The participants' reactions to the objects used by the sick and disfigured models were the same.
They avoided placing the props near their mouths and expressed equal disgust toward the objects, despite reporting influenza as being much more contagious, lethal, and disgusting than the birthmark in a questionnaire.
"The facial birthmark seems to be treated as a disease cue - a false alarm in this case," the researchers write in their study, to be published in an upcoming issue of Evolution and Human Behaviour.
Curtis isn't surprised by the study's results. She says it further establishes that disgust is rooted in disease avoidance.
The work shows how "we are often unaware of the deeper reasons for our actions," adds Justin Park, a psychologist at the University of Bristol in the United Kingdom. And psychologist Mark Schaller of the University of British Columbia, Vancouver, in Canada, notes that the study suggests that these seemingly prejudiced responses may be inborn.
"Even if we know these people are perfectly healthy, our minds are responding to them as if they're not."
So is there anything we can do to change our behaviour? Education is a good start, says Park.
People don't seem to be born with a full catalogue of disease signs to avoid, he says. Rather, we learn what a "normal" appearance is through our experiences.
At the same time, we become more comfortable with something after being exposed to it often.
"So one thing we could do is make atypical appearance more familiar and mundane," possibly by showing people with these types of appearances on television more often, he said.
Additionally, "research shows the initial prejudiced responses [to people with illnesses] tend to be stronger among people who personally feel vulnerable to disease," Schaller said.
For example, people who recently received immunisation against seasonal flu appear to have reduced disease-based prejudices. But this effect could potentially work for other kinds of interventions that make people feel less vulnerable to disease, such as better health care.
"You could make an argument that any kind of society-level public policy that provides a health-related safety net to people would help reduce this problem," said Schaller.
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