Chronic bronchitis affects the bronchial tubes, which bring air to your lungs. It is caused by a long period of smoking or inhating other types of irritants. When you have bronchitis, the glands in your bronchial tubes inflame and begin to release more mucus than usual. The swelling restricts airflow, making it more difficult to breathe. After a while, constant inflammation takes a toll on your bronchial tubes, causing the glands to scar and create permanent damage to the lining of the tubes. Bronchitis is said to be chronic when it goes on for most days of the month for three months for two or more consecutive years, with no other underlying cause.