Chronic bronchitis occurs when the lining of the bronchial tubes repeatedly becomes irritated and inflamed. The continuous irritation and swelling can damage the airways and cause a buildup of sticky mucus, making it difficult for air to move through the lungs. This leads to breathing difficulties that gradually get worse. The inflammation can also damage the cilia, which are the hair-like structures that help to keep the air passages free of germs and other irritants. When the cilia don’t work properly, the airways often become a breeding ground for bacterial and viral infections.

Infections typically trigger the initial irritation and swelling that lead to acute bronchitis. Chronic bronchitis, however, is most commonly caused by cigarette smoking. In fact, over 90 percent of those with the disease have a history of smoking. Inhaling cigarette smoke temporarily paralyzes the cilia, so frequent smoking over an extended period can severely damage the cilia. Chronic bronchitis may develop over time due to this damage.

Secondhand smoke can also contribute to the development of chronic bronchitis. Other possible causes include extended exposure to air pollution, industrial or chemical fumes, and toxic gases. Repeated lung infections may also cause further damage to the lungs and make chronic bronchitis symptoms worse.