One of the most important reasons to keep your air ducts clean is the removal of mold and mildew from your home or business property. Mold and mildew are fungi that can cause physical irritation and even health complications when there is too much of it in your indoor air supply. When you don’t keep your air ducts clean, mold and mildew spores can buildup in the ducts, eventually causing them to be released into the air you breathe on a daily basis.