As some people return to the structures spared from Los Angeles wildfires, experts warn that they should be careful of the air inside and especially cautious when cleaning up. Smoke, ash and all the toxic chemicals that come with both can seep into even well-sealed homes and pose risks to health.

“There’s a lot that has potentially happened to affect poor air quality in your home, even if you haven’t suffered any physical damage to the home itself,” said Katherine Pruitt, national senior director for policy at the American Lung Association. “The fumes and the ash, the particles that are going to be in your indoor environment, are not safe to breathe. You especially don’t want to come into contact with the ash in your lungs, eyes or skin.”

Los Angeles Public Health has declared a local health emergency for the entire county due to the fires. It prohibits the use of air blowers, including leaf blowers, in order to reduce health risks due to the ash and particulate matter from smoke.