Bronchitis, illustration. A sectioned bronchus with excess mucus (yellow) as a result of bronchitis. Bronchitis is inflammation of the bronchi, the tubes which conduct air into the lungs. One symptom of bronchitis is the coughing up of sputum produced within the bronchi in response to the infection or irritation causing the inflammation. The disease also causes shortness of breath because the airways become narrowed. Bronchitis is associated with both smoking and air pollution. With chronic bronchitis there is no cure and the functioning of the lungs steadily becomes reduced.