By guest blogger Laura Spinney

Glastonbury 1997, the 2002 Winter Olympics in Salt Lake City, the pilgrimage to Lourdes in 2008: what do they have in common? All three were the backdrop to outbreaks of communicable disease, and so of interest to doctors working in mass gathering medicine. The goal of this relatively young field is to address the specific health problems associated with mass events, but two British psychologists now claim that this can only be done effectively by understanding the psychological transformation that people undergo when they join a crowd.

Joining a crowd changes a person’s behaviour, say Nick Hopkins of Dundee University and Stephen Reicher of the University of St Andrews, and that change can have both a positive and a negative impact on her health and on the health of those around her. To enhance the former and reduce the latter, they argue, you need to understand both the nature of those changes and the reasons why they happen.

Their argument doesn’t apply to all crowds. It’s not true of the morning scrum on the underground, for example: a physical crowd that happens more by chance or necessity than by design. But it does apply to what they call a “psychological crowd”: that is, people who come together for a specific purpose, such as to listen to rock or to perform a religious ritual, and who in doing so give up their individual identity to adopt the identity of the group, along with its norms and values.

In a study of one of the largest gatherings on earth, the Mela – at which millions of Hindus come together to bathe in the River Ganges in Uttar Pradesh, India – Hopkins, Reicher and colleagues, including Shruti Tewari, detected clear health benefits of the communal experience. Pilgrims self-reported a 10 per cent improvement in their sense of wellbeing, for example, an effect similar to that of some powerful anti-depressant drugs. Those attending such events also described feelings of intense pleasure at being surrounded by others who shared their goals and outlook.

Shared identity may also account for the “collective resilience” that has been observed in the wake of natural disasters, when survivors reach out to help one another because – in these psychologists’ view – they have redefined themselves as survivors of that disaster.

But the same feelings of togetherness that inspire collective resilience can also have harmful consequences, for example exposing people to situations they would normally avoid, and that pose a genuine risk to their health. While writing my upcoming book about the Spanish flu of 1918-1920 (Pale Rider, to be published by Jonathan Cape on 1 June 2017), I came across plenty of anecdotal evidence for collective resilience during the pandemic. In one German town, for example, young women volunteered to nurse strangers in their homes with such enthusiasm that doctors complained they were becoming a nuisance. Such mutual helping behaviour may have been counter-productive in that context because it encouraged the spread of a highly infectious disease.

Normally, disgust would deter us from approaching a coughing, sneezing stranger, but a sense of shared identity can weaken this basic protective mechanism. In 2006, for example, Australian researchers demonstrated the truth of one piece of folk wisdom: that parents find their own children’s nappies less disgusting than those of other children. This was true even when the mothers didn’t know which nappies belonged to which child, meaning that our experience of disgust can be influenced by basic biological relatedness. Earlier this year, Reicher and colleagues expanded on that idea when they showed that the feelings of disgust elicited by a sweaty t-shirt were weaker if people thought the t-shirt belonged to a member of their social group, rather than to someone outside it. They were more tolerant of the disgusting object, in other words, if they believed they shared an identity with its owner.

Translating that finding to the real world, it could help explain why the same survey that identified the disease outbreaks at Lourdes, Glastonbury and Salt Lake City, also counted 15 outbreaks of gastrointestinal infections at mass gatherings from the late 1980s to the present day that were associated – in every case – with non-compliance with hygiene rules. When the gathering in question is on a very large scale, such outbreaks can have serious and long-term consequences. In 1817, for example, there was an outbreak of cholera at the gigantic Kumbh Mela – a sort of mega Mela held roughly every three years – and homeward-bound pilgrims carried the infection throughout East Asia and into Europe, triggering the Asiatic cholera pandemic that raged until 1824.

Harnessing these psychological processes to improve health outcomes at mass gatherings might start with something as simple as an information campaign to remind people about the basic rules of hygiene. In time, perhaps, medics and psychologists could devise more sophisticated ways of enhancing the positive effects of crowds, while reducing their negative ones. It’s early days for such a collaboration, but Hopkins and Reicher believe that the two parties ignore each other at their peril.

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Post written by Laura Spinney for the BPS Research Digest. Laura is a writer and science journalist based in Paris. Her book, Pale Rider, on the Spanish flu will be published in June 2017 by Jonathan Cape in the UK.