Both short- and long-acting β-agonists are used to treat chronic obstructive pulmonary disease. COPD causes airflow limitations in the lungs because of inflammation. Smoking is the main risk factor but inhalation of toxic and harmful particles and gases can also cause the disease. The symptoms are abnormal mucus production, inflation in the lungs that causes airflow limitation, abnormal gas exchange and pulmonary hypertension. COPD is most common in people over fifty who have a long history of smoking. The symptoms are at first mild but worsen over time.