The leading cause of COPD is cigarette smoking. However, long-term exposure to other lung irritants—such as air pollution or chemical fumes—may also contribute to COPD.
When you breathe, air travels down your windpipe into airways. The airways branch into smaller, thinner tubes that end in bunches of tiny air sacs. These air sacs stretch and inflate when you breathe in and deflate when you breathe out.
When you have COPD, your lung function is reduced, with less air flowing in and out of the airways, because of one or more of the following:
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