The Psychology of Disgust

Part 1: The emotion has more far-reaching implications than previously realized.

Posted Sep 16, 2020

When I was in the third year of my undergraduate degree, my classmates and I were tasked with quite a terrible experiment for our microbiology class. We were to fill Petri dishes with agar-agar and nutrients for microorganisms to grow in and take samples from an assortment of places around campus – the cafeteria, the playground, and of course, the toilets. What we found after a couple of days was surprising and, honestly, quite disgusting. I am sure you’ve guessed by now that the cafeteria Petri dishes had more bacterial and other microbial growth than the rest.

What was more surprising, however, is that it took us just about a week or so to get over the results of this experiment and be back in the cafeteria gossiping, eating, and completely forgetting what we’d found. This neat little experiment and its fallouts are more of an illustration of human psychology than anything to do with microbiology. From the point of view of the latter, our study could have been absolutely meaningless given that we just took one sample from each area and didn’t bother repeating the experiment. For all we knew, the results were pure chance.

Or at least, that is what we told ourselves. We needed to rationalize the fact that we could not stay away from the cafeteria for too long. Surprisingly, this wasn’t too difficult: Our brains’ lifelong associations — toilets with dirtiness, and cafeterias with hygiene — were just too strong to overcome.

How disgust governs our actions

These flawed ideas of what is clean versus what is dirty, or disgusting, govern our actions more than we realize. This was the reason scientists during the start of the COVID-19 pandemic (when it still wasn’t clear how low surface transmission risk really was) kept telling us to clean our mobile phones regularly: They knew that something we perceive as “safe” but was in fact a hub of microorganisms would be viewed as less of a threat than the usual suspects. People know on an intuitive level to keep their toilets clean, but not their phones or other high-touch surfaces that “seem” safe.

What makes disgust fascinating as an emotion is that, although it has its origins in protecting the body from ingesting pathogens, its implications are much more far-reaching. From a deep distrust of immigrants with habits different from our own to an avoidance of exotic foods, or to a discomfort with people who have different sexual preferences than our own — disgust is everywhere.

While people like to say that “familiarity breeds contempt," when it comes to the psychology of disgust, it really ought to be the exact opposite. The closer I am to a person emotionally, the less  prone I am to finding them or their habits disgusting.

Paul Rozin and colleagues, in their seminal paper on disgust, discuss the fascinating shift of disgust from merely a protective mechanism against contaminants to a mechanism by which society created rules for moral behavior. The very kinds of phrases we use to describe moral transgressions can give us a clue: Someone who indulges in dirty behavior is a real rotter. Even the facial expressions we use when we smell something disgusting and when we talk about immoral behavior are remarkably similar.

Indeed there is considerable overlap in the brain regions that govern both “core” disgust and moral disgust. When something provokes core disgust, our reaction is to get our bodies as far away from it as possible, to minimize the chances of contamination or infection. Similarly, scientists have suggested that when something disgusts us on a moral level, we tend to want to protect our “souls” from contamination by staying away.

While all this might sound a little far-fetched, there has been a burgeoning of studies over the past couple of decades on the psychology of disgust, what governs it and leads to individual differences, and its implications for society at large.

Categories of disgust

Rozin et al describe four categories of disgust – core disgust, animal-nature disgust (anything that reminds us of our mortal, animal nature – excrement, death, sex), interpersonal disgust (people feel uncomfortable wearing clothes that have been used by another person, especially one who is considered immoral in some way, say, a murderer), and moral disgust (elicited by violations of a “divine code”).

I’ve mentioned “core” disgust a couple of times. What exactly is it? Scientists describe core disgust as a mechanism of food rejection. An entity needs to have a linkage with food, have contamination potential, and also a sense of ‘offensiveness’ in order to elicit core disgust. Every culture in the world eats only a small subset of all potential foods, and they tend to find almost all other foods “exotic” or “disgusting”.

A common way in which people deal with the potential contamination aspect of food is “framing”. When we go out to a restaurant and eat, we are comfortable doing so because the kitchen is out of sight and we don’t have to see a stranger touching our food, and possibly ‘contaminating’ it in any one of a million ways. Out of sight, out of mind.

Disgust and culture

One only needs to meet people from different cultures to realize that, while disgust might be a universal emotion, its elicitors are anything but. For instance, while Americans might find it disgusting that people in other cultures use water to wash themselves after they defecate, other cultures might be repulsed by the fact that Americans use only paper.

Charles Darwin gives an evocative first-person account of how disgust varies across cultures in his book, The Expression of the Emotions in Man and Animals:

“In Tierra del Fuego a native touched with his finger some cold pre-served meat which I was eating at our bivouac, and plainly showed utter disgust at its softness; whilst I felt utter disgust at my food being touched by a naked savage, though his hands did not appear dirty.”

If Darwin couldn’t stomach the idea of a “naked savage” touching his food, the latter could not imagine how meat could be so soft.

This brings us to the fact that disgust isn’t really an automatic or inborn emotion. There is much learning involved. While infants show signs of food rejection (they tend to scrunch up their faces and reject bitter-tasting foods, for example), more ‘sophisticated’ and cultural forms of disgust don’t appear till much later, when children start potty training.

Rozin and Haidt suggest in their paper that one of the reasons for disgust not developing until kids reach a certain age is that adult contamination sensitivity is really quite sophisticated. There needs to be a stretch of imagination to conceive contamination in something that doesn’t really look contaminated: We cannot, after all, see microorganisms (or an imaginary sense of “contamination”) in our food. Children cannot make this leap as easily as adults, which might explain why disgust responses set in a little later in life. Interestingly, studies examining adults and their children’s contamination sensitivities have shown moderate to high degrees of correlation between the two.

In Part 2 of this series, more on what makes disgust sensitivity vary across people and cultures, and the factors that can cause them to vary within individuals.

References

Rozin, P., Haidt, J., & McCauley, C. R. (2008). Disgust. In M. Lewis, J. M. Haviland-Jones, & L. F. Barrett (Eds.), Handbook of emotions (p. 757–776). The Guilford Press.

Charles Darwin. "Chapter 11: Disdain, Contempt, Disgust, Pride, etc., Helplessness, Patience, Affirmation and Negation", The Expression of the Emotions in Man and Animals. New York: D. Appleton & Company. (1872): 253-277.

Curtis V, Aunger R, Rabie T. Evidence that disgust evolved to protect from risk of disease. Proc Biol Sci. 2004;271 Suppl 4(Suppl 4):S131-S133. doi:10.1098/rsbl.2003.0144