Kids across the U.S. are facing more days of wildfire smoke at school.And some buildings are failing to keep dangerous pollution out, according to a new study.Researchers analyzed air quality data from more than 100-thousand schools and 130-thousand childcare centers nationwide.They found the average number of school days with wildfire smoke in the surrounding air rose from about seven a year in 2006 to 54 in 2023.At childcare centers, the annual average climbed from about nine to 112 days.Wildfire smoke can travel thousands of miles, carrying fine particles called PM2.5 that can penetrate deep into the lungs and enter the bloodstream.And being indoors doesn't always guarantee protection.The study also compared indoor and outdoor air quality at 71 West Coast schools and childcare centers.The results: “Some schools had higher indoor PM2.5 concentrations than nearby outdoor measurements during smoke days.”The authors say improved ventilation and portable HEPA filters could help reduce children's exposure.Source: Environmental Research Author Affiliations: Oregon State University .Sign up for our weekly HealthDay newsletter