Chronic Obstructive Pulmonary Disease (COPD) makes it hard for you to breathe. Coughing up mucus is often the first sign of COPD. Chronic bronchitis and emphysema are common COPDs.

Your airways branch out inside your lungs like an upside-down tree. At the end of each branch are small, balloon-like air sacs. In healthy people, both the airways and air sacs are springy and elastic. When you breathe in, each air sac fills with air like a small balloon. The balloon deflates when you exhale. In COPD, your airways and air sacs lose their shape and become floppy, like a stretched-out rubber band.

Cigarette smoking is the most common cause of COPD. Breathing in other kinds of irritants, like pollution, dust or chemicals, may also cause or contribute to COPD. Quitting smoking is the best way to avoid developing COPD.

Treatment can make you more comfortable, but there is no cure.

National Heart, Lung, and Blood Institute