One thing that causes mesothelioma cancer is exposure to asbestos fibers. While the risk of developing mesothelioma increases with the amount of exposure doses, absolutely no level of exposure is safe for human health.
Asbestos fibers are not visible to the human eye, unless in large concentrations. Because they are so small, they are easily inhaled and swallowed by individuals working with or around the substance.
Once inhaled or swallowed, the fibers may penetrate the surface of the mesothelium, a membrane that lines the pleural cavity where your lungs are; the peritoneum, which lines your abdominal cavity; and pericardium or heart sac.
If the fibers that reach these areas are able to damage the cells of the mesothelium, irregular cell division can evolve into malignant tumors. This incurable, and often fatal, form of cancer is known as mesothelioma.