The number one cause of emphysema is cigarette smoking. Smoking activates inflammatory cells in the lung, and causes swelling within the bronchioles and activation of enzymes called proteases that destroy the alveolar wall structures of the lung tissues.
It may also be due to alpha 1-antitrypsin deficiency or A1AD which is genetic. It is a rare condition caused by deficiency of the chemicals that protect lungs from damage by proteases.
Emphysema may also be caused by aging as the lungs lose elasticity, developing small areas of emphysema. Other rare causes are intravenous drug use where drug additives are toxic to lung tissue, immune deficiencies and infections, connective tissue illnesses and indoor air pollution that can damage lungs.