COPD develops gradually over time, often resulting from a combination of risk factors:
tobacco exposure from active smoking or passive exposure to second-hand smoke;
occupational exposure to dusts, fumes or chemicals;
indoor air pollution: biomass fuel (wood, animal dung, crop residue) or coal is frequently used for cooking and heating in low- and middle-income countries with high levels of smoke exposure;
early life events such as poor growth in utero, prematurity, and frequent or severe respiratory infections in childhood that prevent maximum lung growth;
asthma in childhood; and
a rare genetic condition called alpha-1 antitrypsin deficiency, which can cause COPD at a young age.