Did you know that chronic obstructive pulmonary disease (COPD) is the 4th leading cause of death in the United States? It kills more than 120,000 Americans each year—that’s 1 death every 4 minutes—and causes serious, long-term disability. While more than 12 million people are currently diagnosed with COPD, doctors believe another 12 million don’t even know they have it. Learn to recognize the signs of COPD now so you’re not in the dark.

COPD is a lung disease that makes it hard to breathe. It usually worsens over time. In people who have COPD, the airways—the tubes that carry air in and out of your lungs—narrow, making it hard to get air in and out. It can cause coughing that produces large amounts of mucus (a slimy substance), wheezing, shortness of breath, chest tightness and other symptoms.

Airways and air sacs in healthy lungs are elastic—they bounce back to their original shape after being stretched or filled with air, just the way a new rubber band or balloon does. In COPD, the airways and air sacs are damaged, so that they no longer bounce back to their original shape (a condition called emphysema). Or the airways become thicker than normal, with increased mucus production (called bronchitis).

Most people who have COPD are at least 40 years old when symptoms begin. But people younger than 40 can also develop the disease. Unfortunately, most people who are at risk have never even heard of it and, in many cases, don’t even realize that the condition has a name.

“The lung has a lot of reserve, and it takes a fair amount of damage before it produces symptoms,” explains Dr. Gail G. Weinmann, deputy director of the Division of Lung Diseases at NIH’s National Heart, Lung and Blood Institute. “People are probably making adjustments to their lifestyles to accommodate without even realizing it. They often attribute the first symptoms to things like aging, gaining weight or being out of shape. And because of this, they don’t even recognize the symptoms.”

Cigarette smoking is the leading cause of COPD in the United States, but long-term exposure to other lung irritants—such as chemical fumes or heavy dust—can contribute to COPD as well.

“Smokers and ex-smokers account for most cases of COPD in this country,” Weinmann says. “People don’t realize that, even if they quit smoking years ago, they could still be at risk and should talk to their doctors about it.”

The best way to prevent COPD is not to smoke. If work requires exposure to heavy dust, wear protective gear. Try to steer clear of secondhand smoke and other lung irritants that can contribute to COPD.

COPD has no cure. However, treatments and lifestyle changes can help you feel better, stay more active and slow the progress of the disease. That’s why it’s important to recognize COPD if you have it. Then you can take steps to reduce the complications and progression of the disease.

If you think you might have—or are at risk for—COPD, see your health care provider and ask for a simple breathing test called spirometry. To­gether, you can come up with a plan to manage COPD and improve your quality of life.