A new international study has found that even modest short-term increases in fine particulate matter can lead to more coughing, including during sleep. The findings suggest that people living in relatively clean cities may still experience respiratory irritation when air pollution levels fluctuate.
Researchers from the University of Cambridge, Tsinghua University and Sleep Cycle analysed more than 500 days of coughing data from approximately 100,000 app users in 32 cities across 12 countries. Their findings add to growing European health concerns about the effects of air pollution on respiratory health and sleep quality.
What the study found about air pollution and sleep
The research focused on fine particulate matter, commonly known as PM2.5. These tiny particles can penetrate deep into the respiratory system and are produced by sources including road traffic, domestic heating, industry, construction and wildfires.
According to the study, a rise of 10 micrograms of particulate matter per cubic metre was associated with a 2.4% increase in coughing over the following five days. The researchers examined coughing sounds recorded by the Sleep Cycle app, allowing them to study changes in respiratory symptoms over time.
The analysis also considered factors such as weather and influenza levels. Despite accounting for these influences, the association between changing pollution levels and increased coughing remained.
Because many coughing episodes occurred at night, the findings raise concerns about the connection between air quality and sleep disruption. Repeated coughing can interrupt rest, reduce sleep quality and potentially contribute to wider health effects associated with inadequate sleep.
European cities recorded low-to-moderate pollution levels
The study included 13 European cities with average daily PM2.5 concentrations ranging from 5.47 micrograms per cubic metre in Uppsala, Sweden, to 14.70 micrograms per cubic metre in Bergamo, Italy.
The average across the European cities examined was approximately 10.58 micrograms per cubic metre. These figures were lower than those recorded in some highly polluted cities elsewhere in the global dataset, including Beijing and Shanghai.
However, the researchers said that comparatively lower pollution levels did not eliminate the possibility of short-term respiratory effects. The study’s findings suggest that sudden changes in air quality may matter, even when overall concentrations remain below the World Health Organization’s recommended 24-hour guideline of 15 micrograms per cubic metre.
- Uppsala recorded the lowest average concentration among the European cities studied.
- Bergamo recorded the highest European average in the research.
- The European city average was below the WHO 24-hour guideline.
- Short-term increases were still associated with more coughing.
Wildfire smoke produced a stronger effect
The researchers separately examined Los Angeles during its severe wildfire season in 2025. In that setting, a 10-microgram-per-cubic-metre increase in particulate matter was linked with a 10% increase in night-time coughing.
The comparison indicates that extreme pollution episodes, such as wildfire smoke events, may trigger a substantially stronger immediate respiratory response than the smaller fluctuations typically observed in urban environments.
Why night-time coughing matters
Coughing is a normal protective response that helps clear irritants from the airways. Persistent or increased coughing, however, can indicate irritation or inflammation in the lungs.
The study authors cautioned that respiratory symptoms should not automatically be interpreted as evidence of chronic disease. Nevertheless, repeated symptoms may be an early warning sign that warrants attention, particularly for people with asthma, chronic respiratory conditions or other vulnerabilities.
Disrupted sleep may add another layer of concern. Poor-quality rest has been associated with impaired concentration and broader effects on cardiovascular, metabolic and neurological health. The study does not prove that air pollution directly causes these long-term conditions, but it supports further research into the relationship between pollution, coughing and sleep.
What people can do during pollution episodes
The researchers described their work as observational, meaning it identified an association rather than proving direct causation. Even so, people may wish to reduce exposure when local air quality deteriorates.
- Check official air-quality information before exercising outdoors.
- Keep windows closed during periods of heavy smoke or unusually high pollution.
- Use effective indoor air filtration where appropriate.
- Consider a suitable mask during severe outdoor pollution episodes.
- Seek medical advice if coughing is persistent, worsening or accompanied by breathing difficulty.
Advice can vary depending on local conditions and individual health needs. People with existing respiratory or cardiovascular conditions should follow guidance from their healthcare provider.
Limits of the research
The study used data from people who had the Sleep Cycle app, so the participants may not represent the wider population. App-based cough detection can also differ from clinical assessments, and the research cannot establish that every increase in coughing was caused by particulate matter.
Even with those limitations, the scale and international scope of the dataset provide useful evidence about how short-term changes in air quality may affect everyday respiratory symptoms. The findings are particularly relevant as European cities face traffic pollution, winter heating emissions and more frequent smoke events linked to wildfires.
Conclusion
The study’s central message is that relatively clean urban air does not necessarily mean zero respiratory risk. Short-term air pollution increases were associated with more coughing, while severe pollution episodes produced a much sharper rise in night-time symptoms. Monitoring air quality and reducing exposure during pollution events may help protect sleep and respiratory health, but further clinical research is needed to clarify the longer-term consequences.
