Bronchitis - Causes

Chronic bronchitis is caused by inhaling substances that irritate the trachea and bronchi. The most common substance is cigarette smoke. The American Lung Association estimates that 80 to 90 percent of all cases of chronic bronchitis are caused by smoking. Until recently, chronic bronchitis occurred more frequently among men than women because traditionally more men smoked than women. That trend is changing and the number of women suffering from chronic bronchitis is also increasing. Other substances

that can irritate the trachea and bronchi include chemical fumes, air pollution, and other materials in the air, such as mold and dust.

Chronic bronchitis develops slowly over time. It is caused by changes in the cilia (pronounced SIL-ee-uh) that line the trachea and bronchi. Cilia are fine, hair-like projections that wave back and forth, carrying mucus through the airways. Smoke and other irritants can damage cilia, causing them to lose their ability to move mucus normally. The airways become narrow and clogged with mucus. The patient has difficulty breathing because he or she cannot get enough air into the lungs. Eventually chronic bronchitis leads to an even more serious and life-threatening disease, emphysema (pronounced em-fi-SEE-muh; see emphysema entry).