n times of crisis, misinformation abounds. Covid-19 can be cured by ingesting fish-tank cleaning products. Coronavirus was developed in Chinese (or American, or French) labs. Cristiano Ronaldo and the pope tested positive. Why does misinformation flourish? Does all this fake news mean that people are hopelessly gullible, their anxiety making them receptive to the most blatant baloney? Hardly. In many cases, people actually share fake news for fun. We are titillated by gross stories (it all started with bat soup) and celebrity gossip (Ronaldo, the pope). This follows a familiar pattern: in 2018 the most popular fake story on Facebook was about a lottery winner dumping $200,000 of manure on his ex-boss’s lawn, the second most popular about Barbara Bush dying. In any case, believing that Ronaldo has been infected, or that the virus came from a failed biological experiment isn’t all that consequential: it doesn’t make a difference in how we behave. Fans who believed Ronaldo to be sick might still have been thrilled to shake his hand; and no one is besieging virology labs to demand the truth. No, the more worrying fake news regarding Covid-19 is about potential cures. A few days ago, a man died after ingesting a product meant to clean fish tanks, as it contains chloroquine, a drug currently being tested (inconclusively so far) as a treatment for Covid-19, and hailed by some as a miracle cure. But even here, instances of fake news affecting behaviour are very much an exception. Hundreds of millions of people have heard about the supposed virtues of chloroquine, yet such attempts at self-medication remain rare. In the vast majority of cases, people either ignore the supposed curative properties of certain substances, or use them to justify behaviours they wanted to engage in anyway: suspiciously, among the supposed panaceas, we find tea, red meat, alcohol, and even cocaine. Still, even if fake news isn’t as consequential as is often feared, it’s better to be able to spot it (at least to avoid looking like an idiot when sharing on social media). A reliable cue is the source: many successful pieces of fake news circulating on WhatsApp about Covid-19 start with “A friend who has an uncle in Wuhan” or “A friend whose dad works at the Centre for Disease Control.” Such attributions to a (supposedly credible) friend of a friend have always been a staple of rumours and urban legends, and they are a reliable way of telling that a message is bogus. More generally, an online search – about the supposed causes, effects, or cures for Covid-19 – provides reliable information in nearly all cases, especially if several well-recognised sources concur. As in every other crisis situation, the main issue isn’t that people gullibly accept whatever they’re told. On the contrary, the problem is that people fail to absorb recommendations. Again and again, helpful warnings have gone unheeded and advice ignored. Why? People might believe the information is mistaken, or even manipulative. Some mistrust towards politicians is unfortunately understandable, since a number of governments haven’t been fully transparent (and that’s an understatement). Again, this is a pattern: widespread mistrust of officials – among other factors – led 100,000 residents of New Orleans to ignore the evacuation warnings and suffer the full force of Hurricane Katrina’s landfall. The present situation is no exception. The day after the French government announced that all schools would close, and pressed the population to practise physical distancing, my great-aunt – a 96-year-old smoker with chronic lung problems – went to play slots at the casino. Parisian markets were crowded. Even that most emblematic of supposed panic reactions – stockpiling pasta or toilet paper – reflects a lack of trust: a lack of trust in the authorities’ promise that supply lines are sound; and a lack of trust in others to refrain from stockpiling (which makes stockpiling rational for ourselves). Humans are by nature careful about the messages they receive. When evaluating information, we first compare what we’re told (or have read) with our existing beliefs: if it fits, we tend to accept the information. Fake news takes advantage of this by reinforcing our prejudices: drinkers believe that alcohol is a cure, and racists blame Chinese scientists. By contrast, any message that clashes with our personal experience, in particular if it calls for some costly action, is initially rejected. Early warnings were thus, for many, difficult to hear: confinement seemed drastic in reaction to a threat that hadn’t affected us or anyone we knew yet. Overcoming this initial reaction requires trust: a recognition that whoever is addressing us is competent, and isn’t trying to manipulate us. This is why checking information is so important. Not so much because it helps us avoid misinformation: most of us will only be exposed to a tiny amount of misinformation in the first place. Instead, checking is crucial to reinforcing our belief in real news, and in sound advice. If you aren’t persuaded that several healthcare systems are crashing under the strain of Covid-19, that physical distancing is, in many countries right now, crucial, or that you should practise systematic handwashing, please check as thoroughly as you like, but don’t dismiss good advice out of hand. We must strive to be vigilant, but being vigilant is only useful it if helps us remain open to valuable information. • Hugo Mercier is a cognitive scientist at the French National Centre for Scientific Research and the author of Not Born Yesterday: The Science of Who We Trust and What We Believe