Chronic obstructive pulmonary disease (COPD) is a slowly progressive condition characterized by airflow limitation, which is largely irreversible.

Cigarette smoking is the main aetiologic factor in this condition, far outweighing any of the other risk factors. The pathogenesis of COPD is therefore strongly linked to the effects of cigarette smoke on the lungs. There is a general relationship between the extent of the smoking history and the severity of the airflow limitation; however, there is a huge individual variation. The pathology of COPD includes a complex network of inflammation, oxidative stress, tissue damage, remodelling and repair, and these response have significant inter-individual differences such that some smokers do not develop COPD, and some do.