Researching Disgust

Imagine you are in a foreign country and someone puts a cloudy, foul-smelling broth in front of you to eat, with slimy lumps floating in it that look like feces. You probably squinted your eyes, furrowed your brow, and pulled up your cheeks and upper lip. People all over the world understand this facial expression and know what you are feeling right now: disgust.

It is no coincidence that the facial expression for disgust is the same in all cultures. This is because the grimace not only expresses a feeling, but it also changes sensory perception, as researchers at the University of Toronto proved in a study in 2008: The nostrils become smaller and the eyes narrower. This minimizes the amount of disgusting substance inhaled and protects the eyes, the scientists explain.

A useful mechanism. This is because disgust usually evokes things that could make people sick. Hygiene researcher Valerie Curtis from the London School of Hygiene and Tropical Medicine believes that disgust evolved specifically to deal with parasites. These little pests are found all over the world. They harm their host by producing toxins, influencing behavior, consuming resources, and spreading to other individuals in the group.

Whether they are viruses, bacteria, worms, or other creatures, humans are better off avoiding them. That is why, over the course of evolution, barriers such as the skin and mucous membranes have developed to keep such unwanted guests out of our bodies, along with a sophisticated immune system that kills them if they do manage to get in. “Disgust is the third component, the immune system of behavior,” says Curtis. This emotion kicks in before the other two components and is designed to prevent us from coming into contact with pathogens in the first place.

However, because viruses, bacteria, and other parasites are not visible to the naked eye, this “behavioral immune system” must work indirectly. The simplest rules for avoiding parasites would be: Avoid overly close contact with other individuals of the same species. Avoid animals that may carry parasites or look like parasites themselves. Avoid environments and objects that parasites could live on. Disgust causes us to follow precisely these rules. In a survey, Curtis found that infected wounds are perceived as more disgusting than dry ones, a crowded subway is more disgusting than an empty one, and a man showing symptoms of fever is more disgusting than the same man without these signs of illness.

The so-called “contact rule” also supports Curtis' theory: if an object has come into contact with something that causes disgust, then it is itself disgusting. Hardly anyone would want to eat a pizza that a cockroach has walked over. Psychologist Steven Pinker calls this behavior “instinctive microbiology”. After all, pathogens could actually be transmitted through contact. “Disgust is a very sticky emotion, and for good reason,” says Curtis.

This evolutionary biological view of disgust is quite new. For many years, theories that explained disgust primarily as a cultural phenomenon prevailed in psychology. Particularly influential was the view of psychologist Paul Rozin, who also sees disgust as a mechanism for humans to repress their mortality and their kinship with animals. Anthropologist Mary Douglas believed that disgust serves to reject things that do not fit into a culture's worldview, so as not to endanger the social order. And Freud believed that disgust was a learned response and that with targeted education, any activity could be made to trigger disgust. However, studies have shown that the strongest triggers of disgust are the same across many cultures, such as feces, corpses, and pus.

In general, emotions such as anger or sadness are difficult to localize in the brain. Depending on the situation and from person to person, slightly different areas seem to play a role. Neuroscientists who have attempted to locate disgust in the brain in recent years have repeatedly come across two areas: the insula, a part of the cerebral cortex located roughly at the level of the temples, and the putamen, part of the basal ganglia. Patients suffering from Huntington's disease often have damage in these areas of the brain and difficulty recognizing disgust in other people's faces.

British brain researcher Andrew Calder has investigated this phenomenon together with colleagues. They examined a 25-year-old patient with the initials NK, whose insula and putamen had been damaged by a stroke. NK had no fundamental problems recognizing emotions. For example, he was able to pick out happy or sad faces from a series of portraits. Only when it came to disgusted faces did he perform significantly worse than other test subjects. NK was also unable to recognize sounds such as gagging or a sentence read aloud in a disgusted tone as signs of disgust.

Further investigations revealed that NK also appears to feel less disgust. In a questionnaire describing various disgusting situations, he showed significantly less disgust than the control subjects. That is the really important thing about the study, says British psychologist David Perrett from the University of St. Andrews in Scotland: “It shows the connection between the inability to feel disgust and the inability to recognize it in others.”

But there is something else that particularly interests researchers about disgust and raises questions that are extremely difficult to answer: In addition to what researchers call “core disgust,” i.e., the basic disgust triggered by vomit, for example, there is a far more complex form of disgust: disgust at immoral behavior.

In a survey, hygiene researcher Curtis asked 77 young people in the UK about behavior that they find morally disgusting. Rape and necrophilia were mentioned – behaviors that can also be explained in terms of the parasite theory of disgust because of the exchange of bodily fluids and the handling of dead bodies. But among the ten most frequently mentioned behaviors were also discrimination, exploitation, and torture. Do such acts really trigger disgust? Or is it more of a metaphor we use to describe our rejection?

In fact, magnetic resonance imaging studies have shown that immoral behavior activates largely the same areas of the brain as core disgust. For example, an unfair offer in a game stimulates the same facial muscles as looking at disgusting images. Scientists have even been able to show that feelings of guilt about immoral behavior become weaker when test subjects wash their hands. So, it is indeed possible to wash your hands of guilt. Valerie Curtis believes that the brain reacts to signs that another person is behaving like a parasite, i.e., unfairly. Isolating such people because they are perceived as disgusting is a strong punishment for antisocial behavior.

In fact, disgust has also been used as a driver for particularly immoral behavior. The German National Socialists repeatedly justified their crimes by portraying Jews as rats or cockroaches. And in the run-up to the genocide in Rwanda, Hutus denigrated the Tutsis as cockroaches. Labeling people as disgusting seems to be a powerful weapon.

Studies by psychologists Lasana Harris and Susan Fiske of Princeton University at least prove that people can indeed feel disgust toward others. The researchers showed ten test subjects pictures of objects and ten test subjects pictures of businesspeople, students, homeless people, and drug addicts. The results showed that the latter two groups activated the areas of the brain typically associated with disgust. At the same time, the prefrontal cortex, an area of the brain that plays an important role in social situations, was less active. “These neurological findings support the thesis that extreme outsider groups could be perceived as less human or dehumanized,” the researchers conclude in their 2006 study.

However, opinions about outsiders seem to be changeable: when participants in another study from 2007 were asked to consider what food the people in the portraits might like, activity in the prefrontal cortex increased again – according to the researchers, an indication that prejudices can be easily revised and that social perception always depends on context. The evidence for such connections is still very fragmentary, and the activation patterns in the studies could also be explained in other ways. However, the study clearly shows one thing: researchers' interest in one of the most unpleasant emotions in human life has been piqued.

Further reading

• Harris, L. et al.: Social groups that elicit disgust are differentially processed in mPFC. Scan 2. 2007:45 – 51.

First published on July 25, 2011
Last updated on October 25, 2025