Urban air pollution is associated with an increased risk for psychotic experiences in teenagers, researchers report.

A study published in JAMA Psychiatry included 2,063 British teenagers whose health had been followed from birth through age 18. Almost a third of them said they had at least one psychotic experience, ranging from a mild feeling of paranoia to a severe psychotic symptom, since age 12.

Researchers linked air pollution data to locations where they spent most of their time — at home, school or work.

Compared with teenagers who lived where pollution was lowest, those in the most polluted areas were 27 percent to 72 percent more likely to have psychotic experiences, depending on the type of pollutant; exposure to two pollutants, nitrogen dioxide and nitrogen oxides, accounted for 60 percent of the association.

The study controlled for family psychiatric history, maternal psychosis, substance use, socioeconomic status, neighborhood social characteristics and other factors, but it is an observational study that does not prove causation.

“From this one study, we can’t say that air pollution causes psychosis,” said the lead author, Helen L. Fisher, a research psychologist at King’s College London. “The study only says that these things commonly occur together.”