Chronic bronchitis is a long-term condition characterized by a productive cough that discharges mucus. To be considered chronic, the bronchial infection & inflammation, as well as the cough, must occur nearly every day for three months a year for two consecutive years. Smoking cigarettes is the major cause of chronic bronchitis but air pollution, dust, (example - grain elevators), toxic gases and fumes can also be causal factors. Chronic bronchitis can lead to asthma, pneumonia and emphysema and is also called Chronic Obstructive Pulminary Disease, or COPD.

The bronchial tree is the intricate network of passages that supply the lungs with air. When these become infected under acute or chronic bronchitis, the mucous membranes (lining) of the bronchi secrete mucus and pus cells to fight and flush out the infection. This oversupply of mucus causes chest congestion which partially obstructs the airways, making it more difficult to breathe normally. In addition, the irritated membranes may swell, causing further airway obstruction and difficulty breathing.