- Researchers from the London School of Hygiene & Tropical Medicine have identified six distinct types of disgust.
- Among them are rotting food, infected wounds, and risky sexual behaviour.
- Women rated every category more disgusting than men did.
There are plenty of reasons to be a fan of sex. There's increasing evidence that it's good for the brain, and the act of kissing might help us figure out who is biologically compatible with ourselves.
But if you also think sex can be a little bit gross, you aren't alone. In fact, we all probably evolved to feel a certain level of disgust for sexual behaviour, according to new research from the London School of Hygiene & Tropical Medicine.
The new study, published in the journal Philosophical Transactions of the Royal Society, found there are six distinct types of disgust, and women may feel it more than men.
Researchers surveyed more than 2,500 people, giving them 74 potential revolting scenarios - from people with obvious infections, to listening to sneezes and bodily functions in the open - and asked them to rate how disgusted they were on a scale from "no disgust" to "extreme disgust."
The six categories of disgust were atypical appearance, lesions, sex, hygiene, food and animals.
Infected wounds were the most disgusting scenario overall, followed by the violation of hygiene norms, like bad body odour.
Scientists have long recognised disgust as an emotion that evolved to help us avoid infection, known as "parasite avoidance theory," but this new research suggests it is also structured around our social norms.
For example, rotting food could lead to diseases like cholera, and being in close contact with unwashed, unhygienic people could help spread leprosy. Open wounds could spread plague and smallpox.
As for promiscuous sex, historically this could put you at risk of sexual infections like syphilis - still a relatable problem with the recent appearance of super-gonorrhoea.
"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," said Val Curtis, a senior author of the paper and professor at LSHTM. "This type of disease avoidance behaviour is increasingly evident in animals, and so leads us to believe it is evolutionarily very ancient."
The team also found women rated every category more disgusting than men. This is consistent with the fact men tend to indulge in riskier behaviour than women, they wrote. Women found risky sexual behaviour and animals carrying diseases the most disgusting scenarios.
"Although we only really came to understand how diseases transmit in the 19th century, it's clear from these results that people have an intuitive sense of what to avoid in their environment," said Micheal de Barra, psychology professor at Brunel University London and coauthor of the study. "Our long coevolution with disease has 'wired in' this intuitive sense of what can cause infection."