Bronchitis is an inflammation of the bronchial tubes that carry air to the lungs. Chronic bronchitis develops when the airways are irritated over a long period of time, causing excess mucus production. Smoking is the primary cause of chronic bronchitis, as cigarette smoke contains chemicals that damage the airway lining and lead to increased mucus buildup. Treatment focuses on removing irritants like smoking and using medicines to open airways and clear mucus, while the best prevention is avoiding smoking and other lung irritants.