Centuries ago, witches and shamans would mutter curses with the intention of spreading illness. Today, certain social media feeds may serve the same purpose.
We aren’t talking about sharing dubious claims about quack treatments and fad diets, but rather information that exaggerates threats to our health. Through the power of suggestion, these posts can trigger real symptoms – ranging from Tourette’s-like tics to headaches, muscle pain, fainting fits and even cognitive impairment.
Advertisement
That negative expectations can influence our health is already well established – it is called the “nocebo effect” and there is increasing interest in how it can pass from person to person. Scientists have shown that the phenomenon can be highly transmissible, spreading through face-to-face conversations, blogs and – most worryingly – social media.
“Online information can spread nocebo effects faster and farther than has previously been possible,” says at the University of New South Wales in Sydney, Australia. “This is quite scary, given how many people seek health information on the internet and through social media in particular.”
Contagious nocebo responses are so common that you may have experienced one yourself – ever witnessed someone vomit and then felt nauseous? Fortunately, recent research is offering new ways to protect ourselves from these mind viruses.
The placebo effect’s opposite
Even if you have never heard of the nocebo response, you will probably be familiar with its counterpart – the placebo effect. In many situations, this can lead to people feeling better as a result of the mere expectation of relief. presented as a painkiller, for instance, often sees a person’s discomfort evaporating – even though it contains no active ingredient. In the past, we had assumed that these benefits were purely subjective, but research suggests they often result from observable physiological changes. For example, we now know that placebo pain relief coincides with the made in the brain, which work in a similar way to morphine to melt pain away. When you deliver the placebo alongside a compound that blocks opioid signalling, the benefits disappear. The placebo effect is so powerful that people can benefit .
The nocebo response is the precise opposite, describing situations in which our expectations of discomfort become reality. Some of the best examples come from clinical trials: people receiving a placebo treatment not only report some of the benefits of the active drug, but also .
The nocebo response sometimes emerges from shifts in people’s attention. When they are expecting illness, there is a tendency to focus on any feelings of physical discomfort and ascribe it to the pill they are taking. “It puts our antennae up to look for things that are going on in our bodies,” says at the University of Auckland, New Zealand.
Like placebo responses, many are also evident in . For example, when people feel under threat – real or imagined – the body ramps up the production of cholecystokinin, a chemical that amplifies the neural signals that transmit pain. Our expectations may also activate our autonomic nervous system, which is responsible for involuntary responses; this can influence our respiration, blood circulation and bowel movements, resulting in symptoms such as breathlessness, dizziness and nausea. If we are told to expect problems with our brains, we may even .
The consequences can be dramatic. In 2007, for example, a team at the University of Florida examined the experiences of people prescribed finasteride, a drug that is sometimes given to men with an enlarged prostate. Half were told that it could cause erectile dysfunction, half weren’t. Those who were informed of this risk saw , around 30 per cent compared with around 10 per cent.
For a long time, most studies documenting the nocebo response followed a similar procedure, in which an authority figure – such as a doctor – communicates a risk directly to the participant, and then observes how it influences their symptoms. More recently, however, scientists are exploring how negative expectations may spread through “social learning” or via non-formal exchanges.
Contagious headaches
Around 10 years ago, at the University of Turin in Italy to visit a lab at an alpine research facility 3500 metres above sea level. Beforehand, he told just one participant – the “trigger” – that the lower air pressure at that altitude could cause a headache. The trigger was advised to contact the researchers a few days later to confirm the correct dose of aspirin to bring. This instruction was a ruse that allowed Benedetti to identify who else the trigger told about the message.
The trigger soon passed on the advice to their friends, who spread it to their acquaintances, leading 35 other participants to get in touch with the researchers in the run-up to the trip. An altitude headache is a very real risk, but these negative expectations vastly increased the participants’ chances of developing one on their journey up the mountain. Of those had who learned about the warning, around 86 per cent developed the symptoms compared with 52 per cent of those who had not.
Benedetti was particularly interested in the social interactions that had led to negative expectations, and so he asked each participant to estimate the number of times they had discussed the risk. Each conversation appeared to increase the severity of their pain. Taking samples of their saliva at the top of the mountain, he found an association between their symptoms and higher levels of prostaglandin molecules, which increase blood vessel dilation in the brain and are thought to cause headache pain. The gossip had resulted in a measurable physiological change.
Mind viruses
A large body of evidence now confirms the potential for . There may even be chains of transmission, where the nocebo response jumps from person to person like an actual virus – as a 2023 study demonstrated. Led by at the University of Sydney, Australia, it investigated – the nausea that may occur when immersed in virtual reality – in successive rounds of participants who experienced a virtual roller coaster. If one person spoke about their discomfort, the next was considerably more likely to feel it themselves, and they could then pass it on to a third participant, and so on.
What’s more, for reasons that aren’t entirely clear, our sex can influence susceptibility to social contagion. Faasse and her colleagues ostensibly to test the effects of beta blockers, drugs commonly prescribed for heart arrhythmias (the pills were all sham). Some of the participants saw a standard video outlining the potential side effects, such as nausea, headaches, dizziness and muscle fatigue. Others saw a clip of two previous participants, actually actors, describing their personal experiences taking the pills, with facial expressions demonstrating their discomfort.
Witnessing the first-person anecdotes amplified the nocebo response in the female participants, roughly doubling the intensity of the symptoms they experienced. Male participants who saw the anecdotes, however, experienced the same level of nocebo symptoms as men who just saw the standard warning about potential side effects.
Faasse suspects this may be because , and so are more likely to look for social cues for danger. She emphasises that men are still susceptible to nocebo effects through other means, though. In another study, her team that they would experience blurred vision, headaches and nausea from hearing a low-frequency noise. Reading first-person descriptions of the symptoms – the kind of testimonies you might see in a Facebook post or online forum – was enough to trigger them in both men and women equally.
Mass hysteria
Contagious nocebo responses may have contributed to cases of – from the dancing manias of the Middle Ages, which saw groups of people relentlessly shimmying past the point of dangerous exhaustion, to modern mass outbreaks of mysterious symptoms not caused by any infectious agent or environmental toxin.
Thanks to our increasing reliance on the internet, however, information can now pass between concerned individuals at an unprecedented rate. “One of my biggest worries is how easy it is for a short video or a few written comments to generate a nocebo effect, because in the real online world of social media, it’s not just one short video or a few comments,” says Faasse. “If you’re looking for this sort of information, you will find lots of it, and once you’ve engaged with this content, the social media algorithms will show you more and more each time you open the app.”
A steady stream of case reports suggests that we are already witnessing the consequences. Consider the mysterious cases of in the early 2020s, when an increasing number of the platform’s users began to upload videos of facial and bodily tics – to their doctors.
While Tourette’s typically emerges slowly in young childhood, many of these new cases were in people who hadn’t experienced any symptoms before seeing the videos. The sudden onset, combined with the fact that the particular characteristics of the tics – which included whistling, clicking and clapping – were often highly similar to those of a specific influencer, led some neurologists, such as and at the Baylor College of Medicine in Houston, Texas, to conclude that at least some cases had been driven by social media use.
On a much bigger scale, our discussions about covid-19 vaccines may have influenced some of the side effects people experienced after having one of these jabs. at the University of Toledo in Ohio and her colleagues surveyed 551 people over 40 days as they received their first one or two doses of vaccine. The researchers found that both influenced the side effects that people expected and experienced. The more they heard people sharing their experiences, the worse their symptoms.
Social contagion is also thought to lie behind mysterious illnesses such as , the nausea and headaches reported by some people living near wind farms. Many people experiencing these symptoms believe they are caused by infrasound, sound waves at frequencies too low to be audible to humans. However, multiple experiments have found on humans, and point instead to expectations of harm as the real cause of people’s symptoms.
A nocebo response may even explain some cases of food intolerance. Trials of people with have shown that around 40 per cent of them report symptoms even when they have been given a food that doesn’t contain the gluten protein. Though there is still some debate about the origins of NCGS – in some cases, it may be triggered by the presence of other components in wheat besides gluten – studies suggest that the huge amount of cultural attention to wheat intolerance .
Discussions of potential nocebo responses are often controversial, as the water crisis in Flint, Michigan, exemplifies. In 2014, the city switched its water supply from Lake Huron to the Flint river, accidentally exposing residents to lead and other contaminants. Residents were given lead filters and bottled water and by 2016, authorities had reconnected the city to its original source. However, many people were concerned that exposure to lead may have caused cognitive damage, particularly in children. Soon after, the city’s schools witnessed a sharp increase in children being enrolled for support for educational difficulties.
Online information can spread nocebo effects faster and farther than has previously been possible
Although the crisis was no doubt serious, any assessment of its impact is complicated by having to tease apart health problems caused by the contaminated water and by potential nocebo effects. at Rutgers University in New Jersey and at Virginia Tech – who both first helped to raise the alarm over the tainted water supply – recently examined in Flint and Detroit, a city 100 kilometres away. The children had their blood tested for lead multiple times between 2011 and 2019. The analysis showed that the percentage of children whose blood lead levels exceeded the intervention threshold suggested by the Center for Disease Control and Prevention was markedly lower in Flint than in Detroit – which didn’t see a rise in children enrolled in special education – and never rose significantly above Michigan’s statewide average.
Self-fulfilling prophecy
In their report, Roy and Edwards suggested that the consistently negative media coverage about the future prospects of these children “could have created a self-fulfilling prophecy via a nocebo effect”. In , the pair surveyed teachers in Flint, finding that they believed that the children there were “brain damaged” by lead poisoning. Decades of research shows that kids are highly sensitive to adults’ expectations of their abilities and . The teachers’ assessments offered more evidence, they said, that negative labelling of the Flint children might “cause damage that is worse than that caused by the actual exposure to contaminants”.
Edwards says that he has received a hostile response to these findings, however. Some activists are concerned that this explanation undermines the experience of Flint’s citizens, many of whom say they are still witnessing the aftermath of the crisis. Yet Edwards believes that continuing this narrative will do more harm than good. “As a scientist, you have to speak these inconvenient truths,” he says.
The conversation in Flint is complicated by the politics of the original crisis, but scepticism about the nocebo effect is common in many other contexts. “There’s always the suspicion that you’re saying it’s all in their head,” says Petrie, who was a co-author of Roy and Edwards’s paper.
In some cases, people may even interpret a psychosocial explanation of symptoms as an accusation of malingering – but this couldn’t be further from the scientific understanding. Nocebo responses are a natural consequence of the ways our brains work. We may have evolved this trait as a first defence against illness; if others are falling sick in our group, it makes sense for the body to start preparing itself for the threat. These symptoms are in no way fake or deliberate. “The nocebo effect is so powerful, and the symptoms that people are experiencing are real,” says Faasse.
Armed with this knowledge, how do we stop ourselves from falling foul of nocebo’s power?
A greater understanding of the mind-body connection may help to reduce the stigma surrounding the phenomenon and, potentially, arm people against the nocebo response itself. This research is still in its infancy, but a suggest that educating people about the effect appears to reduce the symptoms they report and about the potential influence of the health information that they are consuming.
“Any one of us could experience psychogenic symptoms. I know I have,” says Faasse. “And I think these conversations are part of how we tackle the stigma. If a nocebo researcher can experience nocebo effects, I suspect that anyone can.”
