Chronic obstructive pulmonary disease (COPD) is a lung disease in which the lungs are damaged, making it hard to breathe. In COPD, the airways—the tubes that carry air in and out of the lungs—are partly obstructed, making it difficult to get air in and out.
Cigarette smoking is the most common cause of COPD. Most people with COPD are smokers or former smokers. Breathing in other kinds of lung irritants, like pollution, dust, or chemicals, over a long period of time may also cause or contribute to COPD.
The airways branch out like an upside-down tree, and at the end of each branch are many small, balloon-like air sacs. In healthy people, each airway is clear and open. The air sacs are small and dainty, and both the airways and air sacs are elastic and springy. When a breath is taken, each air sac fills up with air like a small balloon; when you exhale, the balloon deflates and the air exits. In COPD, the airways and air sacs lose their shape and become floppy. Less air gets in and less air goes out because:
The airways and air sacs lose their elasticity (like an old rubber band).
The walls between many of the air sacs are destroyed.
The walls of the airways become thick and inflamed (swollen).
Cells in the airways make more mucus (sputum) than usual, which tends to clog the airways.
COPD develops slowly. It may be many years before symptoms, like feeling short of breath, are experienced. Most of the time, COPD is diagnosed in middle-aged or older people. COPD is a major cause of death and illness, and it is the fourth leading cause of death in the United States and throughout the world. There is no cure for COPD and the damage to the airways and lungs cannot be reversed.