Why is it that a boil bulging with pus fills most of us with revulsion, while a similar-looking cream puff makes us lick our lips? The reason is the interesting emotion known as disgust.
Researchers have long hypothesized that the purpose of disgust in humans and other animals is to keep individuals away from possible infection—an idea called the “parasite avoidance theory.” But as The Guardian's Emine Saner queries: what does this disgust really mean and how does it vary in different people?
According to a new study, most of the things humans find disgusting fall in to six categories, all related to how likely they are to possibly transmit disease.
To dive deep into disgust, Val Curtis, director of the environmental health group at the London School of Hygiene and Tropical Medicine and her team came up with a truly disgusting survey filled with a series of potentially foul scenarios. They then asked over 2,500 participants to rate their level of disgust with each scenario. The research appears in the journal Philosophical Transactions of the Royal Society B.
The scenarios range in grossness and include finding a chicken fetus when cracking open an egg, learning a friend tried to have sex with a piece of fruit, hearing about someone eating road kill rabbits and birds, looking at genital sores, seeing people eat raw fish heads on TV, and finding out your neighbor likes to poop in his backyard.
According to a press release, the results suggest that the scenarios rated most disgusting were related to the historically most threatening disease-causing scenarios. These fell into six broad categories including poor hygiene, disease-ridden animals, sexual behaviors, atypical appearance such as deformity, visible lesions and other signs of infection, and decaying or contaminated food.
Participants rated scenarios involving infected wounds the most disgusting. Violations of hygiene norms, like smelling bad, were also high on list, likely because they could be indicators of disease or infection. It’s no coincidence, the authors write in the paper, that the scenarios most likely to cause transmission of disease are the ones humans find most disgusting.
“The fact we’ve found there is an architecture of disgust that has six components to it tells us something about the way in which emotions work,” Curtis tells Saner. “It tells us that emotions are for doing particular behaviors. The emotion of disgust is about doing certain things that avoid disease—they’re about not eating spoiled food, not sticking your fingers in somebody’s weeping sore, not having sex with somebody you know is having sex with lots of other people, not picking up cockroaches and kissing them. It confirms the hypothesis that disgust really is about avoiding infection.”
One big question, however, is how much of our disgust is innate and how much is culturally conditioned. For instance, the United States is particularly obsessed with getting rid of body odors while Europeans and many cultures around the world aren’t that into deodorant. “The idea of eating from a clean dog bowl is disgusting because of a learned association,” co-author Mícheál de Barra of Brunel University tells Neel V. Patel at Popular Science.
Perhaps the best demonstration of this is the strange case of stinky cheese. As Brian Handwerk wrote for Smithsonian.com last year, a certain percentage of people can’t deal with the smells of some cheeses, many of which are chemically similar to rotten food. For instance, the chemicals that create the scent of Parmesan cheese overlap with those found in vomit.
While the part of the brain that recognizes food lit up when cheese lovers were tested, it didn’t switch on in stinky-cheese haters, meaning they don’t even recognize certain cheeses as food. Currently, it's hard to say if this response is hard-wired, or if the anti-fromagerites learned to hate the cheese.
Debra Lieberman, a professor of psychology at the University of Miami, who also researches disgust but was not involved in this study, tells Patel she thinks the new study gets things mostly right. But she disputes the idea that sexual disgust is mainly about avoiding disease. For one, sexual disgust is much more complex than avoiding STIs and also involves the genetic fitness of potential partners. She points out that other factors can override disgust—for instance, love for a child or parent with open sores can overcome disgust, leading people to care for them.
“Disgust isn’t the only system that governs what how we act,” Lieberman says. “But it does play a major role in three big parts of behavior: eating, touching, and screwing.”
Susan Scutti at CNN reports that the hope is that understanding disgust better will help public health workers and policy makers design campaigns that will motivate people to do things like wash their hands, use toilets and take up other practices that can prevent the spread of disease.