Air Pollution May Be Disrupting Your Sleep, Even At Surprisingly Low Levels

There are plenty of obvious reasons you might wake up coughing in the middle of the night. You're getting over a cold. Your bedroom is dry. Allergies are acting up. Maybe you have asthma.

But what about the air you were breathing hours before you got into bed?

Air pollution doesn't always come with a visible layer of smog or smoke. Fine particles can linger in the air even on days that don't seem particularly polluted, and because they're so small, they can travel deep into the lungs. That exposure may follow us into the night in a surprisingly measurable way.

Researchers from the University of Cambridge, Tsinghua University, and the sleep technology company Sleep Cycle analyzed nighttime coughs from tens of thousands of people using the Sleep Cycle app.

The app uses a phone's microphone to detect sounds like breathing, snoring, and coughing while someone sleeps. Rather than listening to recordings manually, an algorithm identified and counted coughs directly on users' devices. The anonymized data were then grouped by city.

That gave researchers roughly 500 days of data from 32 cities across 12 countries.

Next, they compared nighttime coughing with each city's daily levels of PM2.5, or particulate matter smaller than 2.5 micrometers. These particles are small enough to travel deep into the lungs and have been linked with inflammation and respiratory and cardiovascular problems.

The pattern was surprisingly consistent. For every 10 microgram-per-cubic-meter increase in PM2.5, nighttime coughing increased by about 2.4%.

That might not sound enormous, but remember that this was a population-level change observed across tens of thousands of people. More importantly, the relationship didn't only show up on days with obviously bad air.

Researchers detected more nighttime coughing even when PM2.5 concentrations remained below the World Health Organization's recommended daily limit.

They also had an unfortunate real-world test of the relationship. Los Angeles was one of the cities included in the study, and during the January 2025 wildfires, PM2.5 levels rose sharply. Nighttime coughing climbed alongside them.

A cough is ultimately a protective reflex. Irritation or inflammation in your airways triggers your body to try to clear whatever shouldn't be there. So it makes sense that inhaling more tiny particles during the day could leave your respiratory system irritated hours later.

And while we often think about air pollution as a long-term health issue, this research suggests our bodies may respond to changes in air quality on a much shorter timeline.

You can't control the air outside, but you can be a little more strategic about your exposure when pollution levels are high. Checking the Air Quality Index (AQI) before heading out can give you a quick sense of what you're breathing that day. If the air quality is particularly poor, that might mean moving your long run or outdoor workout indoors, shortening the amount of time you spend exercising outside, or saving it for later in the day if conditions improve.

At home, keeping your windows closed on smoky or high-pollution days can help keep some of those particles outside. Running an air purifier with a HEPA filter, especially in the bedroom, can also help reduce the amount of particulate matter circulating indoors while you sleep.

Sleep and environmental health aren't two separate conversations. The air you breathe all afternoon is still interacting with your lungs when your head hits the pillow that night.