Long-term exposure to certain types of air pollution is linked to an increased risk of Parkinson’s disease, according to a critical review of the existing evidence by researchers at the University of Cambridge.

Air pollution is already a major public health concern, with long-term exposure to fine particulate matter linked to increased risk of stroke and dementia, and implicated in neurodegenerative diseases including Parkinson’s disease, multiple sclerosis, and motor neurone disease. But individual studies have often been underpowered, with inconsistent or inconclusive findings. In a paper published in Environment International, Cambridge researchers carried out a systematic review and meta-analysis — pooling 26 studies on Parkinson’s disease and three each on multiple sclerosis and motor neurone disease — to draw more robust conclusions than any single study could offer.

Two Pollutants, Quantified Risk

The team found two air pollutants associated with increased risk of Parkinson’s disease, which affects approximately 6 million people worldwide: PM2.5, tiny particles small enough to be inhaled deep into the lungs, generated by vehicle emissions, power plants, industrial processes, wood-burning stoves, construction dust, and atmospheric chemical reactions; and PM10, somewhat larger particles from road and construction dust, pollen, mould spores, and vehicle emissions including brake and tyre wear.

For every 5 micrograms per cubic metre of PM2.5, the researchers calculated, an individual’s relative risk of Parkinson’s disease increases by 10 percent — and the average roadside measurement for PM2.5 in Central London in 2023 was 10 µg/m³. For every 15 µg/m³ of PM10, relative risk increased by 18 percent; the average roadside PM10 measurement in Central London that year was 17 µg/m³.

Evidence remained inconclusive for nitrogen dioxide, carbon monoxide, sulphur dioxide, ozone, and soot, largely due to too few studies or inconsistent findings, and the researchers found no evidence linking air pollution to multiple sclerosis or motor neurone disease — though that, too, may simply reflect how little research exists in those areas so far.

“There are still relatively few robust studies that explore the link between air pollution and Parkinson’s disease, but even so, it’s becoming clear that there is a link.”

Dr Annalan Navaratnam, Clinical Research Fellow, IMS Epidemiology, University of Cambridge

A Possible Mechanism

The researchers propose that oxidative stress and neuroinflammation triggered by air pollution, particularly PM2.5, may interact with a person’s genetic susceptibility to Parkinson’s disease, potentially leading to the abnormal buildup of the protein α-synuclein and the loss of dopamine-producing neurons — both hallmarks of the disease.

“These findings add to a growing body of evidence of air pollution’s adverse health effects worldwide.”

Alexandra Tien-Smith, first author, IMS Epidemiology, Cambridge

To help policymakers act on findings like these, Cambridge researcher Dr Haneen Khreis and colleagues have separately built an open-access interactive tool mapping the effectiveness of more than 1,000 policy interventions — congestion charging, mass transit development, electric vehicles, low-emissions zones, and more — for reducing traffic-related air pollution.

“The message is clear: we need to take action now to improve air quality and reduce disease burden globally.”

Dr Haneen Khreis, IMS Epidemiology, Cambridge

The research was partly funded by the European Research Council and the European Union’s Horizon 2020 and Horizon Europe Framework Programmes.

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The study, “Association of long-term outdoor air pollution exposure with incidence of Parkinson’s disease, multiple sclerosis and motor neuron diseases: a systematic review and meta-analysis,” was published July 8, 2026, in Environment International (DOI: 10.1016/j.envint.2026.110377).