Causes

The main cause of COPD is smoking

Other causes include: Second-hand smoke Air pollution (dust or chemicals) Repeated lung infections during childhood Severe asthma Asthma combined with smoking A rare genetic disorder called Alpha-1 antitrypsin deficiency

References:
1. WHO COPD Key facts https://www.who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-(copd)
2. Neil Barnes et al; COPD and exacerbations: Patient insights. BMC Pulmonary Medicine 2013
3. Burudpakee et al; Pulm Ther 2017 DOI: 10.1007/s41030-017-0027-5
4. https://www.nationaljewish.org/conditions/copd-chronic-obstructive-pulmonary disease/overview/lifestyle-management/bring-up-mucus