Scientists have identified six common types of disgust that protect us from disease.
And women rate every category more disgusting than men.
Poor hygiene, animals or insects carrying disease and risky sexual behaviour are among the distinct triggers of disgust that can help humans avoid disease and infection, according to a study led by the London School of Hygiene & Tropical Medicine (LSHTM).
Disgust has long been recognised as an emotion which evolved to help our ancestors avoid infection, but the team has shown the human disgust system is likely to be structured around the people, practices and objects that pose disease risk.
They believe it is the first time the perspective of disease has been used to break up the emotion of disgust into its component parts, and identify six common categories triggering disgust.
The others are skin conditions such as lesions or boils, food that is rotting or has gone off and having an atypical appearance, such as a deformity.
They said their findings could help to target public health messaging, for example to encourage hand washing with soap or to counter the stigma associated with sickness.
The study, which is published in a special issue of the Philosophical Transactions of the Royal Society, saw more than 2,500 people questioned about 75 potentially “disgusting” scenarios they might encounter.
This ranged from people with obvious signs of infection, pus-filled skin lesions and objects teeming with insects, to listening to sneezes and defecation in the open.
Participants were asked to rate the strength of their disgust response to each scenario on a scale ranging from “no disgust” to “extreme disgust”.
Of all the scenarios presented, infected wounds producing pus were rated as the most disgusting. The violation of hygiene norms – such as having bad body odour – was also found to be particularly disgusting.
By analysing participants’ responses, researchers were able to identify the six common categories of disgust, which each relate to regularly occurring types of infectious disease threat in our ancestral past.
The results confirm the “parasite avoidance theory”, in which disgust evolved in animals, encouraging them to adopt behaviours to reduce the risk of infection.
This behaviour is replicated in humans where disgust signals us to act in specific ways, which minimise the risk of catching diseases.
Professor Val Curtis, senior author at LSHTM, said: “Although we knew the emotion of disgust was good for us, here we’ve been able to build on that, showing that disgust is structured, recognising and responding to infection threats to protect us.
“This type of disease avoidance behaviour is increasingly evident in animals, and so leads us to believe it is evolutionarily very ancient.”
The researchers discovered that women rated every category as more disgusting than men, which they believe is consistent with the fact that men are known to indulge in riskier behaviour than women, on average.
The categories women in the study found most disgusting were risky sexual behaviour and animals carrying disease.