COPD is due to an enhanced chronic inflammatory response in the airway and lung to noxious particles or gases. It causes impaired airflow to the lungs. This is due to the airways and tiny air sacs losing their elasticity, the walls between the air sacs becoming destroyed, inflamed, or thick, and the airways producing more mucus than usual causing them to become clogged. COPD encompasses two other clinical phenotypes. The first is emphysema, which is an abnormal enlargement of the gas-exchange airways. The second is chronic bronchitis which is due to a hyper-secretion of mucus and chronic productive cough for at least 3 months of the year or at least 2 consecutive years. Another pathological cause of COPD may be due to an inherited mutation in the alpha-antitrypsin gene, which can cause COPD is young people or non-smokers.