Even low levels of air pollution can increase the likelihood of developing depression or anxiety, a new study from the U.K. found.

The report, published Wednesday in the Journal of the American Medical Association Psychiatry, followed nearly 390,000 adults in the United Kingdom for eleven years, taking into account socioeconomic status and preexisting mental illness. It concluded that long-term exposure to air pollutants at any level can cause greater risk of mood disorders.

“In terms of links to depression and anxiety, those findings have varied depending on the study,” said Cybele Dey, co-chair of Doctors for the Environment Australia via The Washington Post. “There seems to be a link of some kind, but the pathway for how that link is happening is still something we haven’t figured out.”

One possible cause is fine particulate matter, a pollutant that enters the atmosphere when fossil fuels like gasoline, diesel and oil, are burned in vehicles or industrial work. When inhaled, the matter travels deep into lung tissue, where it can enter the bloodstream and contribute to respiratory illnesses, making it the tiniest yet most threatening pollutant.

Air pollution has already been proven to affect physical health, as a 2022 University of Chicago report found that such pollution takes more than two years off the global average life expectancy, making it more dangerous than cigarettes, alcohol, or terrorism.

The link between air pollution and mental health is not as clear, but other studies have linked unclean air to dementia and cognitive decline. Dey's research surrounding the effect of air pollution on children and teens has found “consistent evidence” that air pollution can lead to problems with learning, attention, and focus.

While the United States Environmental Protection Agency recently proposed updated air quality standards, Dey believes that governments need to invest fervently in the transition to green energy, as it could save lives.

“It’s really important for governments to be aware of the impacts,” Dey said. “And conversely aware of the benefits for our health of transitioning off fossil fuels and protecting people from exposure to excessive pollution.”