Asthma is a common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchial spasms. Symptoms include wheezing, coughing, chest tightness, and shortness of breath. Dirty polluted air is known to cause respiratory inflammation. Now exposure to dirty air has been linked to decreased function of a gene that appears to increase the severity of asthma in children, according to a joint study by researchers at Stanford University and the University of California, Berkeley.