Bronchitis is inflammation and irritation of the lining of the bronchial tubes which carry air to and from the the lungs. It causes a cough that brings up thick yellow grey mucus. A cold or flu runs its course till few weeks but sometimes it may spread to the chest causing acute bronchitis which is common but constant irritation or inflammation of the lining of bronchial tubes may cause chronic bronchitis which is more serious.
Chronic bronchitis is one of the conditions included in chronic obstructive pulmonary disease (COPD). The bouts of chronic bronchitis keep on coming again and again.
Few bouts are although harmless but chronic bronchitis can lead to pneumonia and end up into COPD.