Exposure to asbestos could have occurred to people who were actually mining asbestos, people who worked in plants that manufactured goods containing asbestos, workers who were installing asbestos-laden materials in buildings, or those who lived or worked in buildings or homes containing asbestos or products made of asbestos. People who were hired to remove asbestos from a building are also at an increased risk of developing mesothelioma. People who worked with asbestos are more likely to develop mesothelioma than people who were simply around asbestos materials during their every day life.

The level of exposure as well as the amount of time a person was exposed to asbestos also seems to correlate to the risk of developing mesothelioma. For example, someone who worked with asbestos every day for 20 years is much more likely to be diagnosed with mesothelioma than a person who was exposed to it for only one month. However, both categories of exposure contain risk and both can lead to the same cancer. In addition, the younger the person who was exposed, the greater the risk of developing mesothelioma later in life.

Another apparent risk factor for developing mesothelioma is living with a person who has been exposed to asbestos. It is believed that individuals who worked with asbestos materials several decades ago may have unknowingly come home with asbestos particles on their clothing. Because protective coverings were not required on asbestos workers, the possibility of asbestos particles on clothing was a true possibility.

When the particles were taken home on clothing, and the clothes were taken off, the asbestos may have flown into the air inside of the home, and in turn, inhaled by all members of the family. Hence, many family members of past asbestos workers have been diagnosed with mesothelioma. (Today, there are regulations that will not permit a person working with asbestos to leave a facility before showering and changing their clothes.)

It is a mystery as to why some people who had long-term exposure to asbestos in their past never develop mesothelioma, and others who were exposed for only a very brief period of time develop the cancer.

Researchers believe that there may be other reasons that one person is more susceptible to mesothelioma than others. There is a hypothesis that people who develop mesothelioma were born with a gene that makes them more predisposed to cancer. In addition, it has been determined that people who smoke are at a much higher risk of developing mesothelioma if they were also exposed to asbestos at any time in their lives.

There are other mesothelioma risk factors as well. There seems to be a link between mesothelioma and the vaccine that millions of individuals received during the 1950s and 1960s for polio. The connection between mesothelioma and the polio vaccine is only a theory, and there is no scientific proof of this claim.

Another theory regarding mesothelioma's risk factors is related to radiation. Between the 1920s and the 1950s, x-rays, which were used for all sorts of purposes including diagnosing various medical problems, used to contain a substance that was eventually linked to many kinds of cancer. It is believed that there may be a link between those individuals who received x-rays between the 1920s and the 1950s may be at a greater risk of developing mesothelioma than those who were not exposed to x-rays during this period of time.