Disgust

Ekman (1992) defines the emotion of disgust as “experiencing a feeling that motivates, organizes, and guides the perception of thoughts and actions.” In the course of evolution, in fact, emotions have developed to provide new types of motivation and incentive for action to meet the demands of the external environment. In addition, the emotion (in general, not just disgust) also acts as a sensory filter, selecting certain solutions to achieve the objectives set.

Disgust, just like all the other basic emotions such as anger, joy, sadness, and fear, has deep evolutionary value in human history and has played a key role in human survival.

According to the psycho-evolutionary perspective, which develops from the historical work of Darwin, emotions are closely associated with the achievement of universal goals related to the survival of the species. Just think of the role of anxious activation in the recognition of danger and in the triggering of fight and/or flight behaviors.

Within the psycho-evolutionary theory, moreover, emotional facial expressions are considered innate and universal: each fundamental emotion has a specific communicative and expressive configuration, common to all humans and only partially determined by cultural differences (Ekman, 1992).

The existence of universal facial expressions supports the view of emotions as a psychobiological phenomenon rather than as reactions secondary to a cognitive assessment of the situation, based on expectations of what to feel, sometimes influenced by culture (Schacter and Singer, 1962).

The emotion of disgust, whose etymological root refers to “bad taste,” is a basic emotion whose function is to prevent possible contamination and disease (Rozin, Haidt, & McCauley, 1993; Woody & Teachman, 2000).

Darwin himself, in 1872, defined disgust as “something nauseating in relation primarily to the sense of taste,” whether experienced in the moment or remembered. We can therefore define disgust as an emotional defense reaction aimed at preventing the intake of potentially harmful substances through the mouth.

Disgust, in the current literature, is considered a complex emotion of defense against dangers of various kinds and not only as an instinctive form of food rejection. In particular, several types of disgust have been identified:

  • Core disgust (Rozin and Fallon, 1987; Haidt, McCauley, and Rozin, 1994) is the typology that comes closest to the original psychoevolutionary concept referring precisely to the emotion that makes humans more cautious about what they put in their mouths, leading them to reject foods based on their sensory qualities (e.g., unpleasantness) and their history, nature, and origin (who touched them). Core disgust in fact is an oral defense against three different domains of stimuli: food, animals, and bodily products of rejection (feces, urine, saliva, vomit, etc.).
  • Animal reminder disgust (Rozin, Lowery, & Ebert, 1994; Rozin, Haidt, & McCauley, 2000) is a defense against the contact and sight of disgusting objects. This form of disgust is generated through the extension of oral disgust to other sensory modalities, such as touch and sight, and is elicited by objects belonging to the domains of hygiene, death, and violation of the body envelope (wounds, blood, etc.).
  • “Contamination disgust” (Fahs, 2011) refers primarily to disgust reactions triggered by inappropriate or abnormal sexual behavior (based on socio-cultural norms) seen or experienced firsthand. This type of disgust can also result from the sight of or contact with bodily fluids that can be associated with the sexual theme.
  • Interpersonal disgust (Rozin and Fallon, 1987; Haidt, McCauley, and Rozin, 1994) involves contact, either directly or indirectly, with people who are undesirable because they are considered unpleasant and contaminating. For example, physical contact, the sight of, or shared use of objects (clothing, food) with people who are ill, foreign, physically impaired, considered inferior, or guilty of certain crimes may be undesirable.
  • Socio-moral disgust (Haidt, Rozin, McCauley, & Imada, 1997; Rozin, Haidt, & McCauley, 2000), is elicited by moral or social violations, involving brutal acts, enacted by people who are unpleasant and contaminating because they are inhumane. The events judged morally disgusting are very heterogeneous, as they are strongly affected by the cultural influences of each people.

The emotion of disgust appears to play a key role in the phenomenology of many recognized psychopathological disorders, including some specific phobias (e.g., insect-spider, blood-wounding-injection), eating disorders, sexual desire disorders, obsessive-compulsive disorder, and more recently, post-traumatic stress disorder and depression. Within this strand of research on disgust in psychopathology, a large slice of studies explores disgust in the genesis and maintenance of OCD.

The emotion of disgust is in fact at the base of the fear of contamination of Obsessive-Compulsive Disorder (OCD) and often OCD symptoms are structured around the idea of being able to become dirty and disgusting, resulting in avoidance behaviors to prevent the feeling of disgust or possible compulsive behaviors aimed at alleviating the discomfort experienced (Olatunji and Sawchuk, 2005).

Although there is some research that connects disgust with OCD symptoms that are not strictly related to the fear of contagion, such as, for example, religious obsessions (Olatunji et al., 2004), the area that has been most investigated is the involvement of disgust in contamination. Contamination is defined as an “intense and persistent feeling of having been infected, infected, or endangered by contact, direct or indirect, with a person, place, or object perceived as dirty, unclean, infected, or harmful” (Rachman, 2004).

The classic conceptualization of fear of contamination includes only an assessment of threat or danger of infection and the possibility of becoming ill as a result of the contamination itself (Riggs and Foa, 2007). On the other hand, many individuals with contamination OCD are driven by emotions of disgust rather than fear of contagion (McKay, 2006).

The evolution of disgust

In the late 1860s, Charles Darwin hypothesized that the disgust reaction had an evolutionary function. Disgust, he wrote, was innate and involuntary, and had evolved to prevent our ancestors from eating bad food that could have killed them.

Darwin’s theory held that the early humans most prone to revulsion survived by passing down their genes while the more nutritionally daring individuals became extinct.

For many years thereafter, however, scientists paid little attention to disgust. Not until the early 1900s, a decade in which it became fashionable in American television game shows to cover contestants with slimy substances, did disgust attract the attention of psychological and behavioral research. Since then, scientists have identified different types of disgust and studied how they affect our behavior.

The research shows that Darwin was essentially right: disgust is a fundamental aspect of the behavioral immune system, a set of actions influenced by some of the most primal instincts to protect our bodies.

“In terms of health maintenance, disgust is associated with fewer infections, so it’s a useful emotion in relation to disease,” says Joshua Ackerman, associate professor of psychology at the University of Michigan. Researchers found that people more instinctively prone to disgust benefited from this instinct during the COVID-19 pandemic likely because they are more likely than others to attend to hygiene practices such as washing their hands.

However, disgust is a much more complex mechanism than even Darwin imagined. Studies also show that what we find disgusting comes from a set of innate responses and a combination of life experiences that depend on our culture and environment. In addition, for some people, disgust can get to the point of being excessive, preventing us from doing things we think are disgusting but instead help us stay healthy, such as eating fermented foods rich in probiotics.

“It can be a double-edged sword because it’s also associated with revulsion toward unfamiliar things such as food, some of which instead help our health and immune system”Ackerman

Here’s what science tells us about the protective effects of disgust, why some people – particularly children – are prone to feeling disgust at certain things, and the ways humans have hijacked this psychological response to adapt to various cultural norms and achieve interesting health benefits.

Disgust: a protective emotion

The fact that some stimuli are both sources of risk for infection and elicitors of disgust has led many researchers in the field of ethology to theorize that this relationship has a functional role for the survival of animals and humans, especially adaptive in motivating the animal to avoid anything that might infect or infect it (Tybur, Lieberman et al., 2013).

This theory of disgust termed “parasite avoidance” states that the emotion of disgust would allow the animal, through avoidance behaviors, to reduce contact with pathogens or parasites and that this emotion is innate as a defense mechanism (Behringer, Butler & Shields, 2006).

However, this theory has not been unanimously accepted when extended to humans as many believe that disgust may serve as a form of protection from the animal nature that humans are aware of and from their own sense of mortality, as well as a form of preservation of the socially accepted moral order (Rozin, Haidt et al., 2009).

Others, however, believe that the disgust reaction is functionally integrated with the immune system (Schaller, Miller et., 2010) so much so that, especially during pregnancy, a period of increased vulnerability for the contraction of infections, disgust sensitivity tends to increase (Fessler et al., 2005).

Disgust: the study to verify if it is an adaptive signal

If disgust represents a defensive mechanism that produces the implementation of a behavior of avoidance of the pathogenic stimulus, then it follows that there should be specific reactions of disgust against different types of infectious stimuli.

To test this hypothesis, for which disgust would in fact represent for humans an adaptive signal that would allow the whole organism to set up some kind of adaptive and protective behavior in the face of specific potentially harmful stimuli, Curtis and colleagues (2018) investigated by survey the degree of disgust for different items in a group composed of about 3000 volunteers of Caucasian origin, predominantly Anglo-Saxon.

Participants were asked to indicate for each item, created by the researchers based on categories of infectious disease transmission, their degree of disgust, all with the intent of testing the hypothesis that there would be a factor pathogenic structure reflecting different modes of disease transmission (Curtis, de Barra, 2018).

Factor analysis conducted on the data showed that the greatest degree of disgust among participants was specifically induced by these categories of stimuli:

  • hygiene
  • certain animals and insects, such as mosquitoes and rats that carry infections
  • promiscuous sexual behavior that increases the likelihood of contracting a sexually transmitted disease
  • some atypical physical aspects, especially body deformities
  • certain behaviors such as coughing convulsively and breathing abnormally
  • body lesions, particularly on the skin such as pustules, blisters and purulent boils
  • deteriorating foods.

Disgust: it works through vision

The results of the study partially supported the researchers’ initial hypothesis but surprisingly suggested that the items with the highest degree of disgust and potentially harmful were not categorized by people based on abstract, general medical categories of infection risk as previous literature indicated (transmission by fluid contact, through ingestion or fungus) but are categories that can be traced to specific recognizable objects such as purulent boils, blisters, people showing visible signs of illness or poor personal hygiene, and risky practices such as promiscuous sex or ingestion of spoiled food (Curtis, de Barra, 2018)

The categories associate well with the researchers’ view that the “system” would hate to “see” microbes, parasites, or stimuli that have become disgusting as a result of contact with pathogenic microorganisms.

According to Tybur, Çınar, Karinen and colleagues (2018) disgust, in evolutionary terms, has evolved to allow us to survive by avoiding everything that could be harmful and could cause us harm: for example, it has been observed that women consider disgusting some sexually promiscuous behaviors due to the fact that these could increase the risk of contracting sexually transmitted diseases and therefore the risk of seeing reduced reproductive capacity and to carry a future pregnancy.

On the contrary, a research conducted by Simone Schnall (2008), a researcher at the University of Cambridge and director of the Mind, Body and Behavior Laboratory, shows that disgust is not so much related to the prevention of infections or diseases, but it would have the purpose, in some cases, to keep us away from risky activities such as skydiving, downhill rafting, gambling or financial gambling.

In fact, it would seem that people with a high sensitivity to disgust have a greater perception of risk than others with a lower sensitivity to it.

For example, situations that are risky from a social point of view, such as contradicting an authority or talking about an unpopular subject with a superior, could be experienced or perceived by the person experiencing them as uncomfortable and could be considered risky if associated with a high sensitivity to disgust. It goes without saying that the person in question, considering them uncomfortable as risky, avoids them.

Insights

  • Disgust and Obsessive-Compulsive Disorder

References

  1. Behringer, D. C., Butler, M. J., & Shields, J. D. (2006). Ecology: avoidance of disease by social lobsters. Nature, 441(7092), 421.
  2. Curtis, V., de Barra, M. (2018). The structure and function of pathogen disgust. Phil. Trans. R. Soc. B 373: 20170208.
  3. Curtis, V., & Biran, A. (2001). Dirt, disgust, and disease: Is hygiene in our genes?. Perspectives in biology and medicine, 44(1), 17-31.
  4. Fessler, D. M., Eng, S. J., & Navarrete, C. D. (2005). Elevated disgust sensitivity in the first trimester of pregnancy: Evidence supporting the compensatory prophylaxis hypothesis. Evolution and Human Behavior, 26(4), 344-351.
  5. Rozin, P., Haidt, J., & Fincher, K. (2009). From oral to moral. Science. 323(5918), 1179-1180 doi: 10.1126/science.1170492
  6. Schaller, M., Miller, G. E., Gervais, W. M., Yager, S., & Chen, E. (2010). Mere visual perception of other people’s disease symptoms facilitates a more aggressive immune response. Psychological Science, 21(5), 649-652.
  7. Schnall, S., Haidt, J., Clore, G. L., & Jordan, A. H. (2008). Disgust as embodied moral judgment. Personality and social psychology bulletin, 34(8), 1096-1109.
  8. Tybur JM, Çınar Ç, Karinen AK, Perone P. (2018) Why do people vary in disgust? Phil. Trans. R. Soc. B 373: 20170204.
  9. Tybur, J. M., Lieberman, D., Kurzban, R., & DeScioli, P. (2013). Disgust: Evolved function and structure. Psychological review, 120(1), 65.
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