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90% of COPD in the United States is caused by smoking. An estimated 15% - 20% of long-term smokers will develop COPD. Smoking causes the lungs to inflame and the delicate air sacs (alveoli) to be destroyed. This can eventually lead to inflammation and narrowing of the airways (chronic bronchitis), or enlargement of the air sacs, which causes reduced lung elasticity (emphysema).
Other risk factors for COPD include passive smoking, or "second hand smoke" and working or living in heavy air pollution. Although more men have been diagnosed with COPD, the growth of the disease over the past 25 years has been much greater among women than among men. This increase tracks with the increase in smoking among women in the United States since the 1940s. A rare genetic disorder involving an enzyme deficiency called alpha-1 anti-trypsin deficiency (AAT) is also a known cause of COPD in non-smokers. This disorder is responsible for less than 1% of the disease in the United States .
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