If your HVAC systems and air ducts aren’t properly installed and maintained, they can get contaminated with dust, pollen, or other contaminants. Mold and mildew can also grow in your home’s air systems. Some of these contaminants cause allergic reactions.

The EPA recommends cleaning your air ducts if there’s substantial visible mold growth inside sheet metal ducts or if ducts are clogged with excessive amounts of dust and debris.