Exposure to air pollution is linked to higher rates of hospital admission David Grossman/Alamy Stock Photo

Smoggy days are more dangerous than you might think. Even short exposure to fine particulate matter – solid and liquid particles small enough to pass into the bloodstream from the lungs – could lead to higher rates of illness serious enough to require a trip to hospital.

“On average, the days when people are hospitalised have higher pollution than when people are not,” says Francesca Dominici at Harvard University. “What can lead to these little increases can be changes in traffic patterns, increased use of power plants, wind that brings pollution from other areas or wildfires.”

To determine the effect of this pollution, Dominici and her colleagues analysed more than 95 million US hospital records that covered a 13-year period, alongside the concentrations of particulate matter less than 2.5 micrometres in diameter, known as PM2.5, in a patient’s home postal code the day before their hospital visit.


There were 2050 extra hospital admissions and 12,216 extra days in hospital associated with each increase in fine particulate matter by 1 microgram per cubic metre. “Really a very little amount,” says Dominici. Increases greater than this were seen on more than 120 days each year within each postal code during the study years of 2000 to 2012.

Per year, each such increase in PM2.5 could lead to 634 deaths and cost $100 million in hospital fees, the team’s models showed. The increased risk of hospital admission was seen for several conditions, including bloodstream infections, kidney failure, cardiovascular and respiratory diseases, Parkinson’s disease, inflammation and blood clots and diabetes.

The hospital records were from people on Medicare, a type of US government healthcare for people over the age of 65, but Dominici says previous research has shown that PM2.5 exposure has harmful effects on younger people too.

The World Health Organization’s air quality guidelines say PM2.5 should be limited to 25 micrograms per cubic metre. Dominici and her colleagues found that the health risks remain even when they limited their analysis to days within that concentration. The WHO is currently revising its guidelines.

Journal reference: British Medical Journal, DOI: 10.1136/bmj.l6258