A new study has revealed a clear connection between rising air pollution levels and increased night-time coughing, highlighting a hidden health concern that often goes unnoticed. The research, led by Professor Cecilia Mascolo from the University of Cambridge, analysed sleep data collected by a widely-used tracking app, uncovering how airborne particles disrupt rest through persistent respiratory symptoms. While most pollution studies focus on severe health crises, this investigation shines a light on the everyday toll of contaminated air, particularly during colder months and pollution spikes.
Widespread Use of Sleep Technology Reveals Hidden Patterns
The study leveraged anonymised data from a popular sleep-monitoring application, tracking over 98,000 users nightly across 32 cities in 12 countries for 18 months. This approach offered an unprecedented glimpse into population-wide sleep disturbances, with the app also logging coughing episodes throughout the night. According to recent surveys, nearly 40% of UK adults now use technology to monitor their sleep, making such data a valuable resource for public health research. During the observation period, approximately half of all users coughed while asleep, with 1% experiencing more than ten coughs per night.
Pollution Hotspots and Seasonal Variations
The cities with the highest rates of night-time coughing were Milan and Monza, situated in Italy’s notoriously polluted Po Valley. These findings align with broader concerns about air quality in western Europe’s most contaminated regions. Analysis of data from Los Angeles and London revealed that colder weather correlates with increased coughing, as does the presence of circulating influenza. However, the research team emphasised that pollution remained a significant independent factor. “The hardest part was understanding if what we saw in the cough peaks was truly linked to pollution or influenced by viruses and weather,” explained Professor Mascolo.
Wildfires and Fireworks Leave Clear Imprints on Sleep Quality
The study identified several notable pollution events that significantly impacted coughing rates. During wildfires in Los Angeles in 2025, night-time coughing rose by 13%, with some individuals experiencing delayed symptoms. Similarly, in London during November 2025, elevated PM2.5 levels – exceeding World Health Organization guidelines – coincided with a marked increase in cough frequency, despite low flu activity. Professor Mascolo noted that fireworks displays around Guy Fawkes Night may have contributed to short-term air quality deterioration, though source-specific data would be needed to confirm this.
Low-Level Pollution Still Carries Health Risks
Perhaps most concerning, the research found that even in cities with relatively clean air—such as Melbourne and Sydney—higher particle pollution levels correlated with increased coughing. This suggests that current air quality standards may not fully capture the subclinical health impacts of chronic, low-level exposure. Dr Tong Xia, now at Tsinghua University, confirmed that attempts to isolate flu-related influences did not negate the pollution-cough link. “We expected seasonal illness to obscure the relationship, but it didn’t,” he said. The findings underscore the need for ongoing emission reductions, even after legal thresholds are met.
Why it Matters
This study reveals that night-time coughing—a seemingly minor symptom—can serve as an early warning sign of harmful air pollution, affecting billions globally. By tapping into everyday sleep-tracking behaviour, researchers have uncovered a silent public health challenge that extends far beyond hospital visits and emergency cases. The evidence that even moderate pollution levels impair rest and respiratory health demands urgent attention from policymakers and individuals alike. As cities worldwide grapple with air quality issues, this research reinforces the vital importance of sustained environmental action to protect not just physical wellbeing, but also the quality of our sleep and long-term health.