The most important cause of COPD (both bronchitis and emphysema), in about 90% of cases, is cigarette smoking.
Smoking and genetics
Not all smokers develop COPD, suggesting that genetic factors also have an influence on each individual’s risk. The only proven genetic risk factor for COPD is hereditary deficiency of a protein termed α1-antitrypsin. People with this deficiency who smoke may develop COPD in early adult life.
The role of outdoor air pollution as a cause of COPD is unclear, but urban air pollution is harmful to individuals with this condition.
Occupational factors that cause intense or prolonged exposure to dust, chemicals and vapours, etc., can result in COPD, whether a person smokes or not, and increase the risk of the disease in smokers.
Indoor air pollution from biomass fuel has also been implicated as a risk factor for the development of COPD.
Passive exposure to cigarette smoke also contributes to respiratory symptoms and reduced lung function in schoolchildren. In later life, this may lead to COPD.