The leading cause of COPD is smoking, which can lead to the two most common forms of this disease, emphysema and chronic bronchitis. Prolonged tobacco use causes lung inflammation and variable degrees of air sack (alveoli) destruction. This leads to inflamed and narrowed airways (chronic bronchitis); or permanently enlarged air sacks of the lung with reduced lung elasticity (emphysema). Between 15-20% of long-term smokers will develop COPD. Rarely, an enzyme deficiency called alpha-1 anti-trypsin deficiency can cause emphysema in non-smokers. Other risk factors for COPD are passive smoking (exposure of non-smokers to cigarette smoke from others), male gender, and working in a polluted environment.
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