Dear colleagues,

It's time for a snack. How about fried cockroach on a cracker? Or perhaps the Sardinian delicacy casu marzu, a cheese so decomposed that it is infested with live translucent white worms a centimetre long? Be sure to hold your hand over the cheese so the maggots won't jump off.

Try this little exercise. First swallow. Then spit into a clean glass and drink what you just spit. Your saliva is not disgusting when it's in your mouth, but after leaving your body it becomes so.

If you want to know more about the latest research in this area, read Rachel Herz's book That's Disgusting. Just reading her descriptions about potentially disgusting things, such as casu marzu, can arouse an emotional response.

It has long been known that what is disgusting in one culture may be normal or acceptable in another. For example, many Asians find Western cheeses repulsive.

I was surprised to find out that disgust is entirely learned. Babies are quite happy to play with their excrement and to stick all manner of things into their mouths, from dirt to earwax. There are six emotions - happiness, sadness, anger, surprise, fear and disgust - whose associated facial expressions are thought to be recognisable in most cultures. All but disgust seem to be innate. Disgust is a product of human culture.

People vary quite a lot in what disgusts them, and in their overall level of sensitivity to disgust. Herz provides a disgust scale, with 27 statements. For example, you can answer 0 (strongly disagree) to 4 (strongly agree) to statements such as "It would bother me tremendously to touch a dead body" and "It would not upset me at all to watch a person with a glass eye take the eye out of the socket."

Disgust can serve a useful function. It is an alert to avoid certain activities that might be dangerous, such as eating decayed meat. However, too much disgust can be dysfunctional, for example in obsessive-compulsive disorder.

Although disgust is learned, it usually operates unconsciously. Advertisers and politicians can use their knowledge of people's automatic reactions to manipulate them. A famous example is Nazi propaganda against the Jews, associating them with disease and vermin. Racism is often linked to disgust. So is prejudice against people who are HIV-positive or obese.

Herz cites eye-opening research about the operation of disgust. The negative image associated with being fat is contagious: a job candidate who just sits next to an obese person is judged as less capable than one sitting next to someone who isn't overweight.

Feelings of disgust have been traced to a particular part of the brain, the insula. Psychopaths - people without a conscience - have smaller insulas and a lower disgust sensitivity. People with Huntington's disease, which damages the insula, cannot tell whether others are disgusted.

If you're interested in these sorts of matters, you can read what Herz has to say about horror movies, homosexuality, cannibalism, empathy and the fear of death, among many other topics. Her book is engaging and packed with information, all well referenced.

It's worth learning about disgust because it affects our behaviour in ways that are important but which we may not recognise. We might make propositions to others that turn them off. We might set topics in class that offend some students. We might avoid research topics because of the emotions they arouse. We might discriminate against individuals because something about them unconsciously invokes disgust

Just as disgust is learned, so it can be unlearned. If you are repulsed by blood or vomit, you can desensitise yourself through gradually increasing your exposure to it.


Thanks to Paula Arvela, Xiaoping Gao and Tshering Yangden for commenting on the text.


Rachel Herz, That's Disgusting: Unraveling the Mysteries of Repulsion (New York: Norton, 2012)

[Footnotes are omitted from the follow quotes.]

"... you're far likelier to catch something nasty, including staphylococci infections which can cause meningitis, or viruses like the swine flu, from your phone, the lunchroom computer, or by using your local ATM than you would be if you licked the toilet seat in a movie theater restroom. In a four-year study that tested surface samples from five major US cities, it was found that computer keyboards were covered with about 3,295 disease-causing bacteria per square inch, which is four hundred times the amount found on the tops of public toilet seats (only 49 germs per square inch), and that cell phones are technological petri dishes." (p. 94)

"... people can easily be duped by their intuitions and gut feelings, and be led to condemn people even when it is unwarranted. ... Jury members who feel disgusted for any arbitrary reason, regardless of whether they know why they feel disgusted, may be more likely to condemn an innocent defendant or recommend harsher punishment than is deserved. Besides having an upset stomach from the chili at lunch, gut feelings of disgust could arise from superficial characteristics of the defendant himself, such as ugliness, obesity, deformity, or foreignness, or when superfluous information is provided - e.g., that the defendant is homosexual - all of which could lead to erroneous or unduly severe sentencing." (p. 191)

"It has already been established that gore watchers are more likely to be male, and that male psychopaths outnumber their female counterparts by two to one. By contrast, women score higher on measures of empathy than men throughout life, and relative to overall brain size, women have proportionately larger insulas than men do. Women are the more empathic and more disgust-sensitive sex. At the same time, it is interesting to note that empathy can be used for malevolence. A torturer can use empathy to intuit how to increase the victim's suffering. In sports, business, and the social battlefield, empathy can be used to ascertain an opponent's weaknesses and then strategically implemented to manipulate and exploit one's rivals. Maybe this is why women are more psychologically cruel than men - they know what to say and do to hurt the most. It has been well established that both sexes have equal potential for aggression, but that females typically enact their cruelty through psychological and emotional means while males are more physically violent." (p. 224)

"Disgust is not an evil emotion. Disgust is the by-product of being an empathetic and civilized person. You are not 'bad' if you think that eating decomposing shark meat is disgusting, or for being repulsed by the scabby beggar. These things could in fact be accurate signals for disease, danger, and ultimately death. But not all of our disgusts are accurate threats. Being disgusted by immigrants, homosexuals, and drug addicts usually has no physically protective value. Yet it is because we are 'civilized' and live within an integrated social network that we have learned to be, and are socially reinforced to be, disgusted by them. Nevertheless, we can be better than our erroneous disgusts.

Disgust is in our mind and fundamentally under our control. It is our psychology that makes cheddar cheese or casu marzu disgusting or delicious, homosexuality acceptable or not, scatological porn erotic or repulsive, foreigners innocuous or sickening, and our own farts or someone else's humorous or nauseating. We can decide which path to take, or at least ask ourselves why we are feeling the way we do and whether it is useful. We can decide to be disgusted or not." (p. 231)

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