isinformation can be deadly. Tobacco industry propaganda disguising the dangers of smoking; the actions of big oil to undermine the scientific consensus on climate change; corrupt scientists telling parents that life-saving vaccines are unsafe: all have cost lives. And so it goes in a pandemic. “We’re not just fighting an epidemic; we’re fighting an infodemic,” said the director general of the World Health Organization earlier this year. It was prescient. There are people with a clear motivation to spread disinformation regardless of the human cost. There are the corporate interests such as the Conservative donor and multimillionaire hotel owner Rocco Forte, who was given a primetime BBC platform to spread untruths about Covid-19. There are the libertarian thinktanks and politicians who, on principle, resist any regulation that could protect people’s health, such as the American Institute for Economic Research, which has promoted unscientific claims about herd immunity. And there are the shameless populists who will embrace any cause that allows them to consume ever-increasing amounts of political oxygen, such as Nigel Farage. But the most puzzling motivation in the disinformation ecosystem are of the scientists who get caught up in it. In this pandemic, a trio of scientists wrote the “Great Barrington declaration” that claimed that governments can control the spread of the virus simply by segregating the vulnerable and their carers from society. This despite the fact it would be pretty much impossible, and ethically questionable, for 30%-40% of the population to lock themselves away for what at best would be well over a year. This magical thinking has lent a sheen of legitimacy to those who wish to corrupt the legitimate debate about social restrictions with the assertion that they are not needed. Masks are another area where scientists have been co-opted into the disinformation wars. There is growing evidence that masks are effective in preventing the transmission of coronavirus by reducing the risk of mask-wearers who have the virus passing it on to others. First, we are learning more about how the virus spreads, primarily through droplets and aerosols that we all expel into the air by breathing and talking; we know that even quite basic masks can significantly reduce this. Second, observational studies that compare areas where people are required to wear masks in public spaces with those where they are not suggest that masks slow spread. Third, there is little evidence that wearing a mask leads people to engage in riskier behaviour; in fact, wearing a mask seems to be associated with other protective behaviour such as social distancing. So it was perturbing to see Carl Heneghan, a professor of evidence-based medicine at the University of Oxford, claim in a Spectator piece he co-wrote last week: “Now we have properly rigorous scientific research that we can rely on, the evidence shows that wearing masks in the community does not significantly reduce the rates of infection.” He makes two serious scientific errors in his piece, which is based on a misrepresentation of a Danish randomised-control trial. First, the Danish study only considers the impact of mask-wearing on the wearer, not on others. You cannot draw conclusions about the impact of wearing a mask in reducing community transmission based on this study, as its authors make clear. Second, implicit in Heneghan’s piece is the erroneous assumption that there is some abstract hierarchy when it comes to scientific evidence: a randomised trial is always more robust than an observational study. But a randomised trial is only as useful as its design; this particular one was not even set up to answer Heneghan’s question. Attacking the science around masks is just one tactic that the anti-science lobby uses to undermine confidence in public health advice. When Facebook rightly classified Heneghan’s piece as false information, rather than engage with the substance of the critique, he took to social media to tweet: “What has happened to academic freedom and freedom of speech?”, a message shared widely by prominent mask sceptics. Academic freedom does not imply freedom to spread disinformation. But herein lies a clue as to why scientists might end up here. Some of the biggest jumps in scientific progress have come as a result of outlier scientists challenging the scientific consensus: think Galileo, Einstein, Darwin. Unjustified groupthink, particularly where the evidence is fast-emerging, can be very dangerous to science. That means many scientists rightly see an innate value in challenging consensus thinking. Heneghan himself has made some positive contributions as a challenger scientist, for example in asking questions about the way Covid deaths are counted. But challenger science must be based on evidence and data. There is a danger that scientists develop a “Galileo complex” – that they see all scrutiny as akin to the ridicule faced by a scientific giant such as Darwin and cry foul at any challenge. This is evident in the writing of Sunetra Gupta, one of the authors of the Great Barrington declaration, when she conflates fair scrutiny with bullying of a scientific pioneer. It is also evident in Heneghan’s claims that labelling his disinformation as such is an intrusion on academic freedom and in the way he portrays himself as some sort of science crusader in demanding expensive randomised trials on masks. As other scientists drily point out, given the low cost of masks and the “good-enough” evidence base that they are effective, those resources might be better spent on developing vaccines and treatments. The moral of this sorry tale? Trust science, not the scientists. They are only human, subject to the same cognitive biases, the same whims of ego, as the rest of us. In the real world, the line between bravely challenging a lazy consensus and trying to shut down legitimate criticism of bad science can be a thin one. It’s an unnerving realisation, but scientists can be captured by antiscience just like anyone else. • Sonia Sodha is chief leader writer at the Observer and a Guardian and Observer columnist