The Science of Disgust

How Disgust Works (And Why It's Fascinating to Us)

person eating spoon of worms
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Whether it's broccoli, cockroaches, stinky cheese, or the neighbor's kid with a snotty nose, there's something that disgusts you. Chances are good the thing that revolts you is attractive to someone else. How does disgust work and why aren't we all repelled by the same sights, foods, and odors? Researchers have explored these questions and arrived at some answers.

What Is Disgust?

Many children find broccoli to be disgusting.
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Disgust is a basic human emotion resulting from exposure to something distasteful or offensive. It's most often experienced in relation to the sense of taste or smell, but may be stimulated by sight, vision, or sound.

It's not the same as simple dislike. The aversion associated with disgust tends to be so strong that when a disgusting object touches a benign object, the latter becomes "disgusting" as well. For example, consider a sandwich. Most people would be disgusted if a cockroach ran across their sandwich to the point where the sandwich would be considered inedible. On the other hand, few adults (yet many children) would be offended by the sandwich if it touched a broccoli floret.

How Disgust Works

Being disgusted by rotting meat helps prevent accidental food poisoning.
Aviel Waxman / EyeEm / Getty Images

Scientists believe the emotion of disgust evolved to protect organisms from disease. Cross-culturally, objects, animals, and people that appear diseased or that may cause disease are avoided, including:

  • Spoiled foods
  • Animals that are considered to be vermin (rats, mice, fleas, cockroaches, flies, worms, lice)
  • Dead bodies
  • Body fluids (vomit, feces, urine, sexual fluids, mucus, blood, saliva)
  • Visibly unsanitary objects
  • Signs of physical damage (pus, gore, scabs, exposed muscle, and bone)

A response to these stimuli is termed pathogen disgust. Pathogen disgust may be considered to be a component of the behavioral immune system. The emotion is associated with a decreased heart and respiration rate, characteristic facial expression, and an avoidance response. The physical aversion and affect on metabolism may reduce the chance a person may a pathogen, while the facial expression acts as a warning to other members of the species.

The two other types of disgust are sexual disgust and moral disgust. Sexual disgust is believed to have evolved to prevent poor mating choices. Moral disgust, which includes aversion to rape and murder, may have evolved to protect people, both on a personal level and as a cohesive society.

The facial expression associated with disgust is universal across human cultures. It includes a curled upper lip, wrinkled nose, narrowed brows, and possibly a protruding tongue. The expression is produced in blind persons, indicating it is biological in origin rather than learned.

Factors That Affect Disgust

pregnant woman with nausea
bobbieo / Getty Images

While everyone feels disgust, it's triggered by different things for different people. Disgust is influenced by gender, hormones, experience, and culture.

Disgust is one of the last emotions children master. By the time a child is nine years old, a disgusted expression may only be interpreted correctly about 30 percent of the time. However, once disgust has developed, it maintains a more or less constant level through old age.

Women report a higher incidence of disgust than men. Further, pregnant women are more easily disgusted than when they aren't expecting. The rise in the hormone progesterone during pregnancy is associated with an enhanced sense of smell. Scientists believe this helps a pregnant woman avoid threats to a developing fetus. If you're ever uncertain whether milk has soured or meat has gone bad, ask a pregnant woman. She'll almost certainly detect any decay.

Culture plays a significant role in what a person considers to be disgusting. For example, many Americans are disgusted by the idea of eating insects, while snacking on a cricket or mealworm is completely normal in many other countries. Sexual taboos are also cultural.

The Attraction of Repulsion

moldy cheese
kgfoto / Getty Images

If you click through a hundred online gross and disgusting images or are fascinated by gory movies, you're likely normal and not a freak of nature. It's natural to experience a strange attraction to that which disgusts you.

Why is this so? Experiencing disgust in a safe environment, like viewing human parasite photos online, is a form of physiological arousal. Psychology professor Clark McCauley of Bryn Mawr College likens seeking out disgust to riding a roller coaster. The arousal triggers the reward center of the brain. Neuroscientist and psychologist Johan Lundström at the Monell Chemical Senses Center in Philadelphia takes it a step further, stating research indicates the arousal from disgust may be even stronger than the result from encountering something desirable.

Researchers at the Université de Lyon used MRI imaging to explore the neurology of disgust. The study, lead by Jean-Pierre Royet, looked at the brains of cheese lovers and cheese haters after inhaling or viewing different cheeses. Royet's team concluded basal ganglia in the brain are involved in reward and aversion. His team did not answer why some people like stinky cheese, while other detested it. Psychology Paul Rozin, also known as "Dr. Disgust," believes the difference may have to do with negative experiences or with differences in sensory chemistry. For example, the butyric and isovaleric acid in Parmesan cheese may smell like food to one person, yet like vomit to another. Like other human emotions, disgust is complex.

References

  • Curtis, V.; Biran, A. (2001). "Dirt, disgust, and disease: Is hygiene in our genes?". Perspectives in Biology and Medicine44 (1): 17–31. 
  • Irwin M. Marcus; John J. Francis (1975). Masturbation: from infancy to senescence. International Universities Press. p. 371.
  • Oaten, M.; Stevenson, R. J.; Case, T. I. (2009). "Disgust as a Disease-Avoidance Mechanism". Psychological Bulletin135 (2): 303–321.
  • Rozin P, Haidt J, & McCauley C.R. (2000) Disgust in M. Lewis & J.M. Haviland-Jones (Eds) Handbook of Emotions, 2nd Edition (pp. 637- 653). New York: Guilford Press.
  • Wicker, B.; Keysers, C.; Plailly, J.; Royet, J. P.; Gallese, V.; Rizzolatti, G. (2003). "Both of us disgusted in my insula: the common neural basis of seeing and feeling disgust". Neuron40 (3): 655–64.
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