Exercising in Polluted Cities: Is It Doing More Harm Than Good?

Anyone who exercises in a busy city knows the feeling: waiting at a crosswalk mid-run as a van rolls past, leaving a cloud of exhaust to breathe in. For urban runners and cyclists, this is often unavoidable — commutes and workouts frequently mean sitting behind traffic while waiting for lights to change. It raises an obvious question for anyone regularly active in cities: does exercising near polluted roads do more harm than the workout itself provides in benefit? What's Actually in the Air Air pollution has long been linked to chronic conditions including heart disease, respiratory illness, cancer, and a higher risk of premature death. According to the World Health Organization, 99% of the world's population breathes polluted air, contributing to an estimated 6.7 million early deaths annually. Audrey de Nazelle, an associate professor at Imperial College London who studies the effects of pollution on exercise, said the health impact extends well beyond the lungs. She noted that pollution is now understood to affect cardiovascular health, diabetes risk, cognitive function, and even reproductive health, not just respiratory disease. One of the biggest concerns is PM 2.5 — fine particles roughly 30 times smaller than a human hair. Released directly by traffic, these particles can penetrate deep into the lungs, enter the bloodstream, and travel throughout the body. Over time, this exposure can affect brain health as well. A 2025 review analyzing 51 studies and data from more than 29 million people found a link between several types of air pollution, including PM 2.5, and an increased risk of Parkinson's disease. Haneen Khreis, an epidemiologist at the University of Cambridge and co-author of the study, explained that particles this small can cross the blood-brain barrier, damaging blood vessels along the way and ultimately reaching the brain itself. Nitrogen dioxide, another pollutant common near busy roads, was also linked to increased Parkinson's risk in the same review. It's additionally associated with lung inflammation and, over time, can impair lung development and function. Other pollutants of concern include sulphur dioxide, ammonia, carbon monoxide, and ground-level ozone. Why Exercise Intensity Matters Because vigorous exercise increases both breathing rate and depth, runners and cyclists tend to inhale more pollution than walkers covering the same distance — meaning higher-intensity workouts result in a larger dose of harmful particles entering the lungs. Interestingly, sitting in a car doesn't offer much better protection. Rudy Sinharay, a consultant respiratory physician and lung cancer specialist at Imperial College London NHS Trust, said personal pollution exposure while cycling is actually lower than while sitting in a car, partly because cyclists tend to be in motion with more airflow around them. Pollution exposure isn't limited to street-level traffic, either. Underground transit systems in cities like London and New York can carry high concentrations of fine, metal-rich particles generated by friction between wheels, rails, and brakes. The Benefits Still Win Out — Mostly Despite these risks, de Nazelle said the health benefits of exercising in polluted cities generally outweigh the harms, and that exercise itself may help protect the body against some pollution-related damage. In a 2016 modeling study, de Nazelle and colleagues found that the health gains from walking and cycling outweighed the harms of air pollution in most scenarios. The risks only began to approach or exceed the benefits at extremely high pollution levels, such as those found in some of the world's most polluted cities, including Delhi. A more recent review found that exercising in polluted environments was associated with a 26% reduction in mortality risk compared to inactivity — though exercising in cleaner air produced an even greater benefit, reducing mortality risk by 31%. De Nazelle said this should be encouraging for people living in urban areas, though she cautioned that individual medical circumstances matter. People with preexisting conditions such as asthma or cardiovascular disease should exercise more caution when working out in polluted environments. Other research has shown that exercise can still improve lung function, lower blood pressure, and help offset some cognitive effects of pollution exposure, even in polluted settings. How Much Pollution Changes the Equation Still, the degree of pollution matters significantly. In a 2018 study, Sinharay and colleagues had healthy volunteers, along with older adults with chronic obstructive pulmonary disease (COPD) or coronary heart disease, take a two-hour walk either through a park or along a busy London street. Those who walked in cleaner air showed measurable improvements in lung and blood vessel function after just two hours. Those who walked along the polluted street saw smaller benefits, and participants with COPD experienced worse symptoms after exposure. The takeaway, according to researchers, is that exercise helps counteract many of pollution's harms — but heavy pollution also reduces the protective benefits that exercise normally provides, even dulling some of its cognitive advantages. In most cases, the benefits of exercise still outweigh the risks, but exercising in heavily polluted air remains far from ideal. How to Reduce Your Exposure For those unable to relocate to less polluted areas, experts suggest a few practical strategies: Choose quieter routes. De Nazelle said moving just one or two streets away from heavy traffic can reduce pollution exposure by 20% to 30%. One study found that choosing side streets over busy routes cut exposure by as much as 50%. Avoid rush hour. Khreis noted that idling traffic creates concentrated "pollution hotspots," making rush-hour exercise particularly risky. Watch for ozone spikes. Ground-level ozone tends to form during hot, sunny afternoons, and combined with rush-hour pollution, can significantly worsen air quality. Check local air quality indexes. These tools show pollution levels in real time. Sinharay recommends shifting to indoor exercise or parks on days when pollution levels are elevated. Ultimately, experts say individual choices can only go so far. Khreis emphasized that meaningful, long-term improvement depends on systemic policy change targeting pollution at its source, rather than relying solely on personal behavior to reduce exposure. This article is provided for general information only and should not be treated as a substitute for the medical advice of health care professionals.