Unmaintained air ducts and dryer vents can pose serious health hazards, as well as substantially impact energy efficiency. When neglected, air duct build-up circulates more dust, pollen, animal hair, microbes and other contaminants into breathable air inside. Your duct system is a breeding ground for mold, fungi, germs, and microscopic dust mites. Overtime Duct Register Mold Growth causing a serious respiratory illness like allergy, asthma, sneezing and coughing. Air duct cleaning not only has important health advantages to those with asthma or allergies, it also has a positive impact upon the environment.