The hidden legacy of London’s polluted air

Cutting-edge research from the Department of Economic History, LSE. Cutting-edge research from the Department of Economic History, LSE. How did exposure to London’s infamous smogs affect the health of its youngest inhabitants? In his recent article, Born in Smog, Professor Eric Schneider investigates this question using the health histories of children born in London between 1882 and 1919. His findings show that it wasextreme pollution exposure on the day of birth, rather than exposure in utero, thathad lasting impacts on child health. On a foggy morning in early twentieth-century London, the city could almost disappear. The fog entered houses, darkened railway carriages and reduced familiar streets to a few feet of murky air. People lost their way on journeys they made every day. Traffic slowed, accidents increased and the soot suspended in the atmosphere settled on clothes, buildings and lungs. These episodes were not simply natural fogs. London’s cold, still air trapped smoke from millions of domestic coal fires, factories and power stations close to the ground. The resulting mixture of fog, soot and sulphur could turn daytime almost as dark as night. For most Londoners, the immediate consequences were obvious: irritated eyes, difficulty breathing and the practical disruption of moving through a city in which it was impossible to see. But what happened to babies who entered the world during one of these severe pollution episodes? Could the effects of a single polluted day remain hidden for years? It is difficult to reconstruct daily air pollution before systematic monitoring began. But historical observers recorded something closely connected to it: fog. London’s most severe fogs formed during cold, dry and unusually still weather. Without wind or rain to disperse the city’s emissions, coal smoke accumulated near ground level. Evidence from later periods, when researchers could observe both fog and pollution directly, confirms that fog days were associated with exceptionally poor air quality. This makes fog a useful indicator of acute pollution. It also provides a kind of historical natural experiment. Families could not choose whether fog would descend on London during a pregnancy or on the day a child was born. Whether an infant took its first breaths in relatively clear air or in a dense mixture of smoke and fog was largely a matter of chance. I link daily weather observations from Greenwich to two unusually detailed collections of medical records. The first comes fromQueen Charlotte’s Hospitalin Marylebone. Its maternity registers record birth weight and length, prematurity, stillbirth and neonatal death. These records allow us to ask whether exposure to severe pollution before or around birth affected a baby’s condition at the beginning of life. The second source follows children admitted to theLondon Foundling Hospital.Its records document their health from infancy into adolescence, including their heights, weights, illnesses and causes of death. The hospital’s weekly infirmary reports are particularly revealing. From them, I reconstructed more than 6,400 episodes of illness. The reports show not only whether a child contracted measles, influenza or another respiratory disease, but also how long the illness lasted. That distinction matters. Historical studies often focus on mortality because deaths are relatively well recorded. Yet death represents only the most extreme consequence of disease. Children could survive an infection while suffering a longer, more serious illness that weakened them and required weeks of care. The results do not tell a simple story in which every encounter with polluted air damaged every aspect of children’s health. Fog exposure during pregnancy did not reduce birth weight or length. It did not increase prematurity, stillbirth or neonatal mortality. Children exposed to fog around birth were not subsequently shorter or lighter, and they were no more likely to experience common upper-respiratory complaints such as catarrh or tonsillitis. Judged by these conventional measures, the children appeared remarkably resilient. But the longer medical histories reveal something that the measurements taken at birth could not. Children born on foggy days became more vulnerable to serious respiratory disease later in childhood. Between approximately five and ten years of age, they experienced more lower-respiratory illness. When they contracted influenza between the ages of five and fifteen, their illnesses lasted 77 per cent (seven days) longer than those of children who had not been born during a fog. Their episodes of measles lasted 27 per cent longer (four days). There is also tentative evidence that children exposed to fog on the day of birth, or to more fog during their first month, faced a greater risk of dying from respiratory causes later in childhood or adolescence. The timing is striking. I do not find consistent long-term effects from pollution exposure throughout pregnancy or across the postnatal period more broadly. Instead, the day of birth appears to have been an especially sensitive moment. A newborn child suddenly moves from the protected environment of the womb to breathing independently. In London, a baby born during a severe fog may have filled its lungs for the first time with concentrated coal smoke. Such exposure could have damaged the developing respiratory system or altered immune responses, leaving the child less able to withstand infections encountered years later. The surviving records cannot show the precise biological mechanism. Nevertheless, the concentration of the effects in respiratory diseases, rather than health outcomes generally, is consistent with lasting damage to the lungs or immune system. The persistent effects of pollution exposure on the day of birth changes how we should think about the historical costs of air pollution. Acute pollution therefore did more than cause the temporary spikes in mortality documented by other scholars. Exposure at a critical moment could also alter how children responded to disease many years later. The historical setting also matters. Measles, influenza, tuberculosis and other respiratory infections were major threats in early twentieth-century London, while medical treatment was limited. Pollution therefore interacted with an already dangerous disease environment. Evidence from populations living under modern medical and environmental conditions cannot simply be projected backwards into this setting, just as historical estimates cannot be transferred mechanically to the present. At the same time, the persistent health effects were selective rather than universal. Pollution exposure around birth did not affect birth outcomes, child growth or upper respiratory morbidity. Looking across many different dimensions of health therefore produces a more accurate, if less tidy, account of pollution’s burden. London’s fogs were an external cost of the coal-based economy that heated homes, powered industry and helped the city to grow. Some of those costs were immediately visible in darkened streets and choking air. Others only emerged later in life. Born in Smogsuggests that the damage caused by a polluted day did not necessarily disappear when the fog lifted. For children exposed at a particularly sensitive moment, its effects could remain hidden for years, only becoming visible when the next respiratory infection arrived. Read the article in full here:Born in Smog: Immediate and persistent health consequences of acute air pollution exposure in historical London, 1892–1919,Explorations in Economic History,Vol. 101, July 2026 Eric B. Schneider is Professor of Economic History at the London School of Economics and Political Science. His research examines long-run changes in population health, with particular interests in child health, infectious disease and the health consequences of early-life shocks.