Mesothelioma is a disease in which the cells of the mesothelium become abnormal and divide out of control and order. Like with any form of cancer, a genetic mutation causes healthy cells to turn into abnormal cells. Healthy cells normally grow and multiple at a specific rate. They also die eventually, at a specific rate. When the cells become abnormal, the cells grow and multiply out of control and they do not die. A mass of tissue is created by the accumulation of abnormal cells. This mass is what is referred to as a tumor. A tumor may be malignant, which means it is cancerous. With malignant mesothelioma, the abnormal cells invade adjacent tissues and in some instances, they may metastasize (or spread) to invade tissues and organs in other parts of the body to cause damage.

One of nuances of mesothelioma is that the medical community has not been able to identify the specific factors that lead to the initial mutation. As of date, doctors are only able to identify the factors that increase the risk of such a mutation. Asbestos has been identified as the major risk factor for mesothelioma. It is estimated that asbestos is responsible for 70 to 80 percent of all cases of mesothelioma and it could be higher. Though there is consensus in the medical and scientific community that mesothelioma is caused by the inhalation and swallowing of asbestos fibers and dust, there is no medical or scientific explanation for exactly how it occurs.

People who are exposed to high levels of asbestos for long periods of time are most at risk for mesothelioma. However, detectable symptoms of the disease are not immediate. It may take as long as 20 to 30 or even 40 years before symptoms appear. People who live with persons who are exposed to asbestos are also at risk of mesothelioma. This peculiarity is thought to result from the asbestos-based dust and fibers that workers bring into the home in their clothing and other belongings that are exposed at the worksite. Today, workers who are exposed to asbestos are required to shower and change clothes before leaving the worksite.

Though asbestos is directly contributable to mesothelioma, there are many workers who have been exposed to asbestos for years and have never developed mesothelioma. In contrast, there are people who have been diagnosed with mesothelioma and have had only a brief exposure to asbestos. This is another nuance of the disease that leads the medical community to believe that some other factors must play a critical, or at least, contributory role in the development of the cancer.

Some other factors that have been identified as contributory and are being explored include the following:

Heredity  - like with other forms of cancer, some people may inherit certain traits and characteristics that cause them to be more susceptible to mesothelioma.
Smoking - smoking has been shown to significantly increase the risk of mesothelioma in people who have also been exposed to asbestos.
SV40 - simian virus 40 (SV40) is a virus that was traditionally found in monkeys, but may have been transferred to humans who received polio vaccinations in the 1950s and 1960s. During this time, the polio vaccine was developed with monkey cells. Since that time, SV40 was thought to be linked to certain cancers and was removed as a component of the vaccine. Some research indicates that SV40 may also be passed between individuals, but it is not conclusive. 
Radiation- X-rays that were performed from the 1920s to the 1950s included a radioactive substance known as thorium dioxide. The substance has since been identified as a cause for cancer and it is no longer used in radiation.
Zeolite- zeolite is a naturally occurring mineral that is similar to asbestos. This mineral is used primarily in Turkey in the construction of homes. Research suggests that zeolite is directly related to cases of mesothelioma in Turkey.