HUMANS, like other animals, have evolved to notice and avoid sources of infection, whether that be rotten food or sickly members of their own species. This “behavioural immune system” can have unexpected consequences. Studies have, for instance, shown that those whose noses are more easily offended are also more likely to shun foreigners or disapprove of homosexuals. More broadly, people who live in regions with more to fear from pathogens tend to be less promiscuous and gregarious (such risky behaviour may spread disease). These effects are, by their nature, generally small but evidence has been amassed that they do in fact exist.

This led Marco Liuzza of the Magna Graecia University of Catanzaro, in Italy, and his colleagues to wonder whether there might be a link between a person’s sensitivity to malodorousness and the likelihood of them being sympathetic to right-wing authoritarian views. In work published this week in Royal Society Open Science, he shows that there is.

Members of the team have developed a body-odour disgust scale (BODS). This is based on asking volunteers a series of questions about different scenarios, such as noticing that a friend’s feet smell. From this it can be established how strongly, on a scale of one to five, a person reacts to bad smells. To see if this ranking reflected a person’s authoritarian leanings, the team recruited 201 volunteers through Amazon Mechanical Turk, a website where people from all over the world carry out small tasks in exchange for cash.

Passing the smell test

The volunteers completed the BODS questionnaire and others that gauged the extent to which they sympathised with certain authoritarian views (“Our country needs a powerful leader, in order to destroy the radical and immoral currents prevailing in society today”, for instance) and with more socially, fiscally or morally conservative views. The researchers found that those scoring highly on the BODS scale did indeed hold more authoritarian views. They found no such correlation between the BODS score and more broadly conservative opinions.

As their work was being conducted in 2016, when Donald Trump’s campaign to become president of the United States was in full swing, the researchers wondered if such a relationship would hold true for Americans. If so, would there be any hint of an increased sensitivity to bad smells among his supporters?

To test this idea, they recruited 159 more participants solely from the United States and repeated the experiment. They found a similar pattern with their American volunteers: those sensitive to bad smells tended to hold authoritarian views. The effect was small, enough to explain between 4% and 16% of the difference in viewpoints (family background, economic circumstances and other factors would presumably account for much of the rest).

Last, the team recruited more Americans to test whether the BODS score would tell them anything about voting intentions in the presidential election. Expecting an even weaker correlation this time, they used 391 participants in the hope that they would be able to discern an effect, if it were there. They did indeed find such a relationship. High BODS scores were a feature of those intending to vote for Mr Trump, but not the Democratic Party’s nominee, Hillary Clinton. This time, however, the association was even weaker—enough to account for only about 1% of voting intention.

A tiny effect, but an effect nevertheless. The work of Dr Liuzza and his colleagues adds to the persistent evidence suggesting that prejudices and political views can be influenced by a person’s desire to avoid disease and bad smells.