Bronchitis is an inflammation of the inside surface of your bronchial tubes, which carry air to and from your lungs. Usually results from an URI (upper respiratory infection) that somehow makes it deeper into the respiratory tract causes inflammation, swelling, and mucous production on the bronchioles. People who have bronchitis often cough up thickened mucus, which can be discolored. Bronchitis may be either acute or chronic. Chronic bronchitis, a more serious condition, is a constant irritation or inflammation of the lining of the bronchial tubes, often due to smoking.