Bronchitis is an inflammation of the bronchial tubes, or bronchi. Bronchi are the air passages that extend from the trachea into the small airways and alveoli. Viruses, bacteria, parasites, smoking, or inhalation of chemical pollutants or dust may cause inflammation. During an episode of acute bronchitis, the cells of the bronchial-lining tissue are irritated and the mucous membrane is hyperaemic and oedematous, diminishing bronchial mucociliary function. Consequently, the air passages become clogged by debris and irritation increases. In response, copious secretion of mucous develops, which causes the characteristic cough of bronchitis.

Chronic bronchitis may result from a series of attacks of acute bronchitis, or it may gradually evolve because of heavy smoking or inhalation of air contaminated with other environmental pollutants. When so-called smoker's cough is continual rather than occasional, the mucous-producing layer of the bronchial lining has probably thickened, narrowing the airways to the point where breathing becomes increasingly difficult. With immobilisation of the cilia that sweep the air clean of foreign irritants, the bronchial passages become more vulnerable to further infection and the spread of tissue damage.

Acute bronchitis:

• Cough that produces mucous
• Burning sensation in the chest
• Sore throat and fever
• Fatigue/weight gain
• Cyanosis
• Wheezing