Bronchitis is a condition where the lining of the bronchial tubes becomes infected and inflamed. During bronchitis the amount of oxygen and air that flows into the lungs gets reduced and it causes phlegm or heavy mucus to form in the airways. Bronchitis starts as a condition where the cell linings of the bronchi get irritated and the tiny hairs which are called cilia that trap and eliminate the outsides things stops working. This condition is further aggravated when the materials associated with inflammation also increases and clogs the passage of air.

Bacteria, virus and other particles which irritate the bronchial tube are the main reasons which start bronchitis. Acute bronchitis is mainly caused by the virus which is similar to that of flu and cold. Besides this exposure to tobacco smoke, pollutants and solvents, gastroesophageal reflux disease can also start acute bronchitis. Chronic bronchitis on the other hand starts due to cigarette smoking and it can also be caused by the continuous attack of acute bronchitis.

Other conditions like toxic, air pollution, dust, gases and industrial fumes may also result in bronchitis. In most common conditions bronchitis starts as a secondary infection following an upper respiratory infection like cold. The defining symptoms of bronchitis includes productive cough which brings green or yellow mucus.