Disgust protects people against infection
According to researchers, disgust as a human emotion has evolved to help protect us against infectious diseases.
Val Curtis, PhD, BSc, MSc, director of the environmental health group at the London School of Hygiene & Tropical Medicine, and Mícheál de Barra, PhD, lecturer in psychology at Brunel University London, identified six cues for disgust that they said have historically helped humans avoid infection.
According to their study published in Philosophical Transactions of the Royal Society B: Biological Sciences, responses to these sensory stimuli — such as the sight of a person with boils on their skin or the smell of rotting food — work as protective mechanisms.
“It is fascinating to see that disgust has an internal structure that helps us to avoid categories of things that might have made us sick in our evolutionary history,” Curtis told Infectious Disease News. “It must have been good for our ancestors to avoid contact with these six types of things, including lesions, poor hygiene and spoilt food.”
Curtis and de Barra surveyed more than 2,700 people to gauge their reaction to 75 vignettes — potentially “disgusting” situations they might face, such as encountering people with clear signs of infection, seeing pus come from a genital sore, noticing a lamp covered in insects, seeing someone sneeze phlegm into their hands, feeling someone breathe on them or learning that their neighbor defecates in his backyard garden instead of a toilet.
The situations were presented in writing beside a 100-point sliding scale with “no disgust” at one end and “extreme disgust” at the other. Participants clicked along the sliding scale to indicate the degree of disgust prompted by each vignette.
Using the responses, Curtis and de Barra isolated six common triggers of disgust — hygiene, sex, atypical appearance, lesions, food and animals — each of which correspond closely to historical causes of disease. They said their findings support the so-called “parasite avoidance theory,” which holds that disgust is an evolutionary response that animals developed to reduce their risk for infection.
The survey identified gender differences in reported disgust levels. Women, who made up 66% of respondents, rated all six categories of disease stimuli more disgusting than men. In particular, they were disgusted by risky sexual behavior and diseased animals.
“Whilst women and men are mostly similar in their disgust, there is about a 12% difference that is significant,” Curtis said. “That may be because in the evolutionary past, women passed on more genes by being extra disgusted to protect themselves and their children. Men are known to take more risks, because on average they end up with more offspring that way.”
Curtis and de Barra believe more research on humans’ disease-avoidance systems can improve public health.
“If we understand the categories of things we instinctively avoid, we can build on that,” Curtis said. “For example, we found that people would wash their hands with soap more often in a public toilet where we put up a message that said ‘Don’t take the toilet with you.’ We can build on that disgust of poor hygiene.” - by Jennifer Byrne
Disclosures: The authors report no relevant financial disclosures.