The most dangerous form of asbestos is naturally found in sheaths of rodlike fibers. These fibers by their structure break into smaller and smaller pieces. Serpentine asbestos is comprised of curly fibers. The serpentine asbestos when breathed in are usually caught in the outer areas of the respiratory system. When fibers are inhaled, most are cleared in the nose, throat, trachea (windpipe), or bronchi (large breathing tubes of the lungs) by sticking to mucus inside the air passages and being coughed up or swallowed. The long, thin, fibers are less readily cleared, and they may reach the ends of the small airways and penetrate into the pleural lining of the lung and chest wall. These fibers may then directly injure mesothelial cells of the pleura, and eventually cause mesothelioma.
The risk of lung cancer among people exposed to asbestos is increased by 7 times compared with the general population. Peritoneal mesothelioma, which forms in the abdomen, may result from coughing up and swallowing inhaled asbestos fibers.
