COPD mainly involves chronic bronchitis and emphysema, and asthma can also coexist and overlap with COPD in many people. These conditions together cause long‑term breathing difficulty and irreversible airflow obstruction in the lungs.
Three diseases in COPD
Clinically, COPD is “the name for a group of lung conditions” that almost always includes:
- Chronic bronchitis – long‑term inflammation of the bronchi with excess mucus.
- Emphysema – damage and destruction of the air sacs (alveoli), reducing surface area for gas exchange.
- Asthma – not formally a subtype of COPD, but asthma can coexist and converge with COPD, often referred to as asthma–COPD overlap.
How smoking leads to COPD
Cigarette smoking is the main cause of COPD, responsible for the vast majority of cases in high‑income countries and around 9 in 10 cases in some national data. Smoke contains thousands of chemicals and very high levels of oxidants that irritate and inflame the airways and lung tissue over many years.
This chronic irritation triggers persistent inflammation in the central and peripheral airways and in the lung parenchyma, leading to structural “remodelling” of the small airways (narrowing, scarring) and destruction of alveolar walls (emphysema). The result is mucus overproduction, loss of elastic recoil, airway collapse on exhalation, and “air trapping,” which together cause the fixed airflow limitation that defines COPD.
