The composition of a wildfire can also have an impact on human health. With the California fires engulfing homes and businesses, smoke in the region is likely carrying chemicals released from synthetic building materials that are more toxic than those emitted from burning vegetation.

Particles from wildfire smoke can be much smaller than the width of a human hair. They are dangerous because they can be inhaled and travel deep into the lungs and enter the bloodstream, the EPA says. They can cause respiratory irritation and shortness of breath, and they can make conditions worse for people with asthma and heart disease.

In laboratory experiments, a given amount of wildfire smoke causes more inflammation and tissue damage than the same amount of air pollution, according to Kent Pinkerton, co-director of the Center for Health and the Environment at the University of California, Davis.

Exposure to wildfire smoke is a growing health problem across the U.S., as climate change increases the risk and intensity of wildfires.

Firefighters are still struggling to control the blazes, which have led to wildfire smoke that’s worsening the air quality in the region.Wildfire smoke can travel long distances and affect the air quality far beyond the immediate vicinity of the fire.

Incinerating commercial and residential buildings releases hazardous chemicals and gases from their materials.