One of the main causes of COPD is prolonged exposure to cigarette smoke, especially if the smoke is inhaled. However, breathing in second hand smoke, air pollution, chemical fumes and dust from the environment or workplace can also cause COPD⁴.
These inhaled particles cause the mucus glands that line the bronchi to produce more mucus than normal. The particles also trigger inflammation, which cause the walls of the bronchi to thicken and swell. Environmental factors and genetics may also play a part in the development of COPD⁴⁻⁵.