The primary factor for mesothelioma risk is asbestos exposure. The use of this material has been banned in the United States since around 1975, but there are about 8 million Americans that may already have been exposed through various jobs, such as miners, ship builders, factory workers, railroad workers, mechanics and construction workers (particularly those responsible for installing brakes in automobiles and insulation in buildings). Many men and women who served in the Navy have been exposed to significant amounts of asbestos on their ships.

The material asbestos is not only found on the job or in the workplace. It may also be found in 10-15% of public schools (about 110,000) throughout America. Asbestos fibers and dust have also been known to be picked up through clothing or other articles. After exposure to the airborne fibers or dust, the risk of lung cancer is 7 times greater than that of the general population (smokers who are exposed to asbestos have a risk that is 50-90 times greater still).

And not all of the workers that have been exposed to asbestos will develop diseases related to their exposure. In fact, many workers will experience no ill effects or symptoms.

The asbestos that is bonded into many finished products such as walls, tiles, and pipes poses no risk to our health as long as it is not damaged or disturbed (for example, by sawing or drilling) in such a way as to release fibers into the air. When the asbestos particles are set free and inhaled, however, exposed individuals are at risk of developing one or many of the asbestos-related diseases. Once these fibers work their way into body tissues, they may stay there indefinitely.

The health risk of developing asbestos-related diseases varies with the type of industry in which the asbestos exposure occurred and with the extent of the worker's asbestos exposure. In addition, different types of asbestos fibers may be associated with different health risks. For example, results of several studies suggest that workplace exposure to amphibole forms of asbestos are more likely than exposure to chrysotile asbestos form to cause lung cancer, asbestosis, and, in particular, mesothelioma. Even so, no asbestos fiber type can be considered harmless, and proper safety precautions should always be taken by people that work under threat of asbestos exposure.