A new international study suggests dirty air may be showing up in a way many people notice but rarely discuss: more coughing in the middle of the night.
Here's what to know
Researchers spotted the pattern in heavily polluted northern Italy and during major smoke events in Los Angeles, California, the Guardian reported.
Using anonymized information from a sleep app, the researchers assembled a dataset spanning 18 months, 32 cities, 12 countries, and about 98,000 people on a typical night. In addition to sleep patterns, the app logged how often users coughed overnight.
Across those day-to-day records, higher particle pollution was linked to more nighttime coughing. Overnight coughing was common in the sample: About half of users reported coughing, and 1% coughed more than 10 times.
The highest coughing rates were seen around Milan and nearby Monza in Italy's Po Valley, a part of western Europe known for especially polluted air.
More background
Cecilia Mascolo of the University of Cambridge, who led the study, said air pollution research often focuses on symptoms serious enough to prompt medical care, which can make everyday effects go unnoticed.
TCD Picks » Quince Spotlight
💡These best-sellers from Quince deliver affordable, sustainable luxury for all
"I come from an area in Italy with very high pollution, and I am very aware of its not-talked-about effects," Mascolo told the Guardian.
For their analysis, the team worked to separate pollution from other likely causes of coughing. In Los Angeles and London, the data showed more coughs in colder weather and during periods when flu was circulating, but the pollution connection remained even after those factors were taken into account.
Short-term pollution spikes provided some of the clearest evidence.
"The L.A. wildfires were the clearest and most severe pollution spike in our study window," Mascolo said.
Wildfire smoke exposure was tied to a 13% increase in nighttime coughing.
What can be done?
The study found effects at concentrations below World Health Organization air-quality thresholds, suggesting legal compliance should not be treated as the finish line.
It also adds to the evidence that lower pollution remains a worthwhile goal even in places where overall pollution levels are relatively low.
Finally, the findings point to the value of symptom tracking and suggest sleep tech may be capturing real environmental patterns, not just bedtime habits.
Where can I learn more?
These stories show how air pollution is affecting health in different settings:
• Across Europe, air pollution levels have improved over 20 years, but health risks remain.
• In Lahore, smog pushed residents toward masks as pollution levels soared dangerously.
• In Delhi, breathing outdoor air was likened to smoking half a pack of cigarettes.
• Polluted air poses heart and mental health risks, adding pressure for stronger public protections.
• Indoor cooking and heating can create serious health consequences when biomass smoke builds up.
Get TCD's free newsletters for easy tips, smart advice, and a chance to earn $5,000 toward home upgrades. To see more stories like this one, change your Google preferences here.
