An analysis of air-quality data from more than 100,000 U.S. schools and 130,000 childcare centers found that smoke-affected days increased substantially from 2006 to 2023.

Over that period, the average number of smoke-affected days rose from about seven to 54 a year for schools, and from about nine to 112 for childcare centers.

Wildfire smoke can travel thousands of miles, and its fine particles can penetrate deep into the lungs and enter the bloodstream, meaning indoor spaces do not always shield children from exposure.

A separate comparison at 71 West Coast schools and childcare centers found that some had higher indoor PM2.5 levels than nearby outdoor readings on smoke days.

Researchers said coordinated preparedness plans, indoor air-quality monitoring, activity changes during smoke events, improved ventilation and portable HEPA filters could help reduce children’s exposure.