Emphysema is very rare in people who have never smoked. It is the complete obstruction of the bronchioles, with increased resistance to air passage, especially during expirations. Thus, rupture of the walls of the alveoli may occur, with formation of large cavities. This decreases the lung's efficiency in absorbing oxygen and there is an overload of the heart to compensate for lung deficiency. Overloading causes most emphysema patients to die of heart failure.
Smoking is the leading cause of lung cancer, 80% of this cancer could be prevented if people stopped smoking. Several substances contained in cigarettes are carcinogenic. Cancer cells that originate in the lungs multiply uncontrollably and may invade other tissues in the body, where new tumors originate.