Most cases of COPD occur as a result of long-term exposure to lung irritants that damage the lungs and the airways.
In the United States, the most common irritant that causes COPD is cigarette smoke. Pipe, cigar, and other types of tobacco smoke also can cause COPD, especially if the smoke is inhaled.
Breathing in secondhand smoke, air pollution, and chemical fumes or dust from the environment or workplace also can contribute to COPD. (Secondhand smoke is smoke in the air from other people smoking.)
In rare cases, a genetic condition called alpha-1 antitrypsin deficiency may play a role in causing COPD. People who have this condition have low levels of alpha-1 antitrypsin (AAT)—a protein made in the liver.
Having a low level of the AAT protein can lead to lung damage and COPD if you're exposed to smoke or other lung irritants. If you have this condition and smoke, COPD can worsen very quickly.