Bronchitis Bronchitis is an inflammation of the bronchial lining. It is commonly related to cigarette smoking but is also triggered by environmental irritants such as chemical vapours, exhaust fumes or pesticides. In response to the inflammation, excess mucus is produced. This can block the small airways and reduce respiratory efficiency, for example, in chronic airways obstruction. Over-production of mucus leads to frequent coughing, which further irritates the tissues and causes even more mucus production