What causes mesothelioma?

Asbestos is a major known cause

Studies show that asbestos is a major cause of mesothelioma. By various estimates, it accounts for about 75–80% of all mesothelioma cases in the United States. Asbestos is a mineral that occurs as a long, thin fiber in the environment. Before its usage was banned due to health dangers in the 1980s, it was used in many industrial and insulation materials as a fire retardant. Some of the jobs in which people have been exposed to asbestos directly or indirectly are those that involve factory work, demolition, insulation, shipbuilding, carpentry, and installation of brake linings in vehicles. Despite rigorous efforts to eliminate asbestos from our environment, some public and private buildings still contain asbestos. Personnel who remove asbestos from such structures or work around asbestos are required to wear personal protective equipment to lower their risk of exposure.

Asbestos fibers may be inhaled and become lodged in the lungs, which can cause damage. If swallowed, asbestos may lead to peritoneal mesothelioma. Scientists are still researching exactly how asbestos fibers cause mesothelioma. It may be by a direct action on the cells of the body or by forming substances that affect genes in the body.
There may be other causes

Although asbestos is the major cause of mesothelioma, up to 30–50% of all cases are not obviously related to prior asbestos exposure. Other possible causes include prior exposure to radiation or to certain minerals closely related to asbestos that are found in the soil. Smoking has not been shown to be a cause of mesothelioma. However, if a smoker has also been exposed to asbestos, this greatly increases his or her risk of developing other types of lung cancer.