The leading cause of lung disease is cigarette smoking. Ingredients in
smoke paralyze the cilia, change the mucus secretions, and interfere
    with the work of the macrophages, thus leaving the lungs vulnerable to
physical damage and infection. Inflamed and irritated bronchi produce
increased and thickened mucus, a condition known as bronchitis.
 Acute bronchitis often accompanies viral infections. Chronic
bronchitis results from constant irritation; the stagnant mucus in the
bronchi invites recurring infections and other diseases. Prolonged
irritation or infection also causes emphysema, air trapped in the
alveoli, resulting in shortness of breath. Chronic bronchitis,
emphysema, and several similar diseases, collectively known as
 chronic obstructive pulmonary disease (COPD), affect 9 million
people in the United States and are directly responsible for 45,000
deaths a year. Moreover, they are the fastest rising cause of death.
 Lung cancer, claiming nearly 120,000 lives a year, is strongly
associated with cigarette smoking. Other common diseases are
pneumonia, an inflammation with extensive airways congestion from a
variety of causes; asthma, an allergic constriction of the bronchi; and
 pneumoconiosis, a disease category that encompasses chronic
irritations from industrial dusts such as those from coal, cotton, and
stone.