Risk Factors.The number one risk factor for mesothelioma is working with asbestos. A history of asbestos exposure is present in nearly all cases. However, mesothelioma has been reported in some individuals without any known exposure to asbestos (rare).

Asbestos. Asbestos is the name of a group of metamorphic minerals that occur naturally as masses of strong, flexible fibers made up of hydrous magnesium silicate. The natural resistance to fire is the major reason why asbestos has been exploited for a variety to uses. Asbestos has been widely used in many industrial products, including cement mats and fabrics, brake shoes and gaskets, roof tars and shingles, flooring plasters and stuccos, adhesive textiles, and fireproofing insulation.

During the manufacturing process, tiny asbestos particles may be inhaled or swallowed, causing serious health problems. Exposure to asbestos increases the risk of lung cancer, asbestosis (noncancerous), mesothelioma and other cancers in the airway passage. Smoking does not appear to increase the risk of mesothelioma itself. However, the combination of smoking and asbestos exposure significantly increases the risk of developing cancer of the lungs.

Types of Asbestos. Asbestos is typically categorized into 2 subgroups. The serpentine group is derived from serpentine rocks that yield curled, corkscrewed fibers that are more soluble. The amphibole group is straight and needle-like.

• Serpentine Group. Chrysotile is the white asbestos that is most often used in the United States. Because chrysotile is less friable that other asbestos types, it is less likely to be inhaled. There is some controversy to whether chrysotile fibers, when inhaled, can cause mesothelioma. It is now thought that this form of white asbestos is indeed harmful but not to the level that amphiboles are hazardous.
• Amphibole Group. The amphibole group of asbestos fibers include amosite (brown asbestos), crocidolite (blue asbestos), tremolite, actinolite and anthophylite. These asbestos types are easily friable. For this reason, a single, large amphibole rock can easily break into millions of smaller needle-like fragments that are primed for inhalation. The crocidolite form from Africa and Australia is considered to be the most dangerous type of asbestos. Due to the deadly nature of these fibers, asbestos from the amphibole group was banned in the U.S. in the mid-1980s. However, due to the ready supply and cheaper cost, some unscrupulous companies continued to use amphiboles for construction pipes, casings for communications, and thermal insulations. This has lead to expansion of mesothelioma litigation in the United States

Some History. Since the late 1800s, asbestos has been mined and used commercially. With more industrialization, its use greatly increased (especially during World War II). Since the early 1940s, millions of American workers have been exposed to asbestos fibers when the risks associated with asbestos exposure were not known. Over time, an increased risk of developing mesothelioma was found among shipyard workers, people who worked in asbestos mines, producers of asbestos products, and workers in the heating and construction industries. Today, the U.S. Occupational Safety and Health Administration (OSHA) sets limits for acceptable levels of asbestos exposure in the workplace.

Epidemiology. Studies have associated exposure to asbestos with the development of lesions in the airway. Though not completely clear in all cases, it is thought that asbestos contributes as insoluable foreign bodies that the body forms a reaction to. The result is often a series of physical signs such as asbestos bodies in the sputum, pleural plaques, diffuse pleural fibrosis, asbestosis, carcinoma of the lung, gastrointestinal tumours and diffuse mesothelioma of the pleura and peritoneum.

The duration, the intensity and the reoccurance of exposure is thought to play a role in increasing the risk of developing mesothelioma. This is sometimes misleading, however, as there have been cases in which incidental, short-term exposure has resulted in mesothelioma. Likewise, not all people that have been exposed to asbestos have developed disease. This just goes to show that the development of mesothelioma may not necessarily have a risk threshold.

Evidence has shown that some family members (as well as other co-inhabitants) of asbestos workers have an increased risk of developing mesothelioma. It is thought that this increased risk may be the result of exposure to asbestos dust brought home on the clothing and hair of asbestos workers. To reduce the chance of exposing family members to asbestos fibers, asbestos workers are usually required to shower and change their clothing before leaving the workplace.