Why are dirty air ducts so common? A lack of proper ventilation can cause harmful particles to accumulate in the ductwork, which can then be discharged into the atmosphere. Other factors that can contribute to dirty air ducts include dust, animal dander, and pollen. If left untreated, these particles can cause respiratory problems, including asthma. Luckily, there are many ways to clean and maintain your ductwork to minimize the risk of exposure to these pollutants.