That's Disgusting

Everyone has one, something they find disgusting; whether it is a crawling insect, body odor, or a bruised banana. But setting aside, for the moment, the actual source of disgust, why is that such a universal experience? As it turns out, understanding the thinking behind disgust has a long scientific history, a recent paper in Philosophical Transactions of the Royal Society sought to determine whether disgust protected us from infection.

In the last 100 years, disgust has been categorized in many ways, from Freud’s defense against inappropriate behavior to more generalized belief that disgust might be protective against disease. There is some evidence that disgust upregulates our immune system and women in their first trimester of pregnancy, a vulnerable period, show heighten disgust sensitivity. The researchers sought to determine if disgust protected us from infectious disease by looking at our response to disease vectors, like bad food, sneezing or open sores. They categorized 14 behaviors, generated multiple vignettes and elicited whether they were felt to be “disgusting” through an online survey involving about 2500 people – mean age 28, 66% women and predominantly from the United Kingdom.

They did not find statistical proof that associated disgust with vectors of disease. The categories of disgust they identified: 

• Poor personal or environmental hygiene – sniffles, an unflushed toilet
• Animals – disease vectors like crawling insects, cockroaches, raw chicken
• Sexual – promiscuous behavior 
• Atypical appearance – missing limbs, heavy wheezing, a hairless cat
• Skin lesions – signs of infection like pus, genital sores
• Food – signs of spoilage bruised, mushy fruit or vegetables, the green texture on meat

They believed that these categories reflected signals to initiate “protective” avoidance behaviors. And this makes some greater sense than their original hypothesis. Our understanding of disease transmission by bacteria and viruses, objects we cannot readily see with the naked eye, is relatively new, but there is an evolutionary advantage to avoiding situations with a higher likelihood of contamination and disease. These categories of disgust are cues to those circumstances. As they wrote

…categorization makes sense from the point of view of a pathogen detection system that could not ‘see’ microscopic pathogenic microbes and parasites. Instead, selection operated on behavioural avoidances of specific categories of people, practices, and objects. 

There were some gender variations, as you might expect, men generally had a higher threshold for disgust than women. Women and men differed the most regarding animal and sexually related disgust and the least over atypical appearance. Increasing age diminished disgust except for the poor hygiene category. 

Their discussion ends with an intriguing consideration, is there a tradeoff that can alter the disgust response? For example, does food disgust diminish in the face of hunger? For atypical appearance, men and women did not differ in their disgust as they did on all of the other categories; could this be a greater nurturing effect among women? Does the attenuation of disgust with age represent experience?

This was a gentle reminder of how complicated we are and how integrated our behavior is with the environment. “Going with your gut,” is more than just an old saying. Emotions provide behavioral cues, even when the feeling is disgust.

Source The Structure and Function of Pathogen Disgust Philosophical Transactions of the Royal Society DOI: 10.1098/rstb.2017.0208