Southwyck House in South London is a block of flats so intimidating that it is often mistaken for a prison. Locally known as the Brixton ‘barrier block,’ it has a stark exterior of brick and concrete that literally looms over you, giving the impression that unseen people are staring down through the sparse rectangular windows.

It was built as a social housing project, designed to shield its residents from the noise of a phantom motorway that was intended to run from Blackheath to Battersea. The road was never built due to petty political squabbles, but the building now stands as a seven-story barricade against its illusory traffic.

If you’re not used to the built-up environment of the inner city, the block can certainly feel unsettling. But here, urban alienation may run deeper than mere architecture. The area was found to have the highest rate of diagnosed schizophrenia in a large study of South London, even when compared with directly adjacent neighborhoods.

The research that found this striking variation was led by epidemiologist James Kirkbride, now at University College London. Kirkbride’s work is but one in more than a century of studies that have found higher rates of psychosis in cities and which have sparked an intense debate over whether—to put it in its original terms —‘cities cause madness’ or whether those affected by ‘madness’ just tend to end up in cities.

The link between psychosis and city living was first noticed by American psychiatrists in the early 1900s who found that asylum patients were more likely to come from built-up areas. This association was sporadically rediscovered throughout the following century until researchers verified the association from the 1990s onwards with systematic and statistically controlled studies that tested people in the community as well as in clinics.

One particularly extensive study using health records for almost the entire population of Denmark found that the risk of being diagnosed with schizophrenia increased in a small but proportional way as people spent more time spent living in urban environments. Many studies have since replicated this finding, with neighborhood levels of social deprivation seeming to amplify the association and levels of social integration seeming to reduce it.

To many, this provides evidence that cities are universally bad for our mental health—something that chimes with a strong cultural belief that associates the natural world with tranquillity. It might seem like common sense that living in a run-down, inner-city neighborhood would wear away at your psychological wellbeing. But here is where the cultural cliché breaks down, because the effect is surprisingly selective.

The data shows that urban environments reliably increase the chances of being diagnosed with schizophrenia or having related experiences like paranoia and hallucinations. This is not the case for other mental health problems primarily caused, for example, by depression or mood instability. If it was a general effect on wellbeing, you would expect the chance of being diagnosed with any mental health problem to increase at an equal rate, but this isn’t the case.

There are good reasons to think that city living might be the cause of some of these problems. The two big psychological negatives of city living, social isolation and social threat, are already well studied in mental health. They are risk factors for a range of psychological difficulties but have been particularly associated with misperceptions and paranoia. And for people who are already experiencing paranoid delusions, there is good evidence that urban environments amplify anxieties, increase the intensity of hallucinations, and weaken self-confidence.

But none of this conclusively proves that cities cause schizophrenia and some argue the causal arrow actually goes round the other way. People with psychosis, the alternative explanation goes, are just more likely to end up living in poor city neighborhoods—something first labeled the ‘social drift’ hypothesis.

Originally, this was a simple stereotype of someone hitting ‘rock bottom’ due to the disabling effects of psychosis. But we know this can’t explain what we see in modern studies because time spent in the city is also associated with your future chance of developing these experiences. A recent study led by Joanne Newbury at King’s College London even found this effect in children, who have little say where they live.

A more nuanced take is that the same factors that increase your chance of getting diagnosed with schizophrenia also increase your chances of ending up in living in a deprived urban area. Poverty and neglect might be the obvious candidates but a recent study led by Oxford University epidemiologist Amir Sariaslan using more than two million Swedish health records suggests the effect can be better explained by shared genetic risks which could be common across the whole family.

The idea that genetics could influence something so complex as finding a house might seem counter-intuitive but Sariaslan explains that it is best understood in terms of limiting life choices rather than affecting decision making. “Living in a deprived neighborhood in adulthood partly reflects academic achievements and labor market position, which are in turn largely influenced by cognitive abilities, impulsivity and personality traits” he says, “[all of] which have all been found to be moderately to considerably heritable.”

Kirkbride welcomes the study but cautions against a solely genetic explanation for the high risk of psychosis in more urban, deprived communities. He adds that even if genetic factors are involved in shaping where people live, “it is only through improving our social environment that we can reduce the additional burden of mental health, and break the cycle of socioeconomic disadvantage often faced by families living in such neighborhoods over successive generations.”

For those of us who live in cities, the cause of the urban psychosis effect remains comfortably unconfirmed, but the scientific interest is having wider reaching consequences. Des Fitzgerald, a sociologist at Cardiff University who studies the social impact of neuroscience, has described how this scientific question is motivating researchers to work across disciplinary boundaries with an intensity rarely seen before. Social scientists are turning to biology to understand the impact of cities, and neurobiologists are now becoming interested in the neuroscience of the urban environment.

Fitzgerald highlights how studying the city is pushing psychiatry researchers to think more widely about what are too commonly pigeon-holed as environmental factors. “You just can't talk about social life without some accounting for its richness, its complexity, its contests, its ambiguity” says Fitzgerald. “If there's going to be a meeting point anywhere” he says, “I think, it's there.”