A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs. Having a known risk factor, or even several risk factors, does not mean that you will get the disease. And some people who get the disease may not have had any known risk factors.

These are the well known risk factors for the development of mesothelioma cancer:

1-Asbestos :

The main risk factor for developing mesothelioma is exposure to asbestos. In fact, most cases of mesothelioma have been linked to asbestos exposure in the workplace.

Asbestos refers to a family of fibrous minerals made of silicate. It is a naturally occurring mineral that can be found in dust and rocks in certain parts of the United States and other parts of the world. There are 2 main forms of asbestos:

1-Serpentine (curly) fibers include chrysotile, the most widely used form of asbestos.
2-Amphiboles are thin, rod-like fibers. There are 5 main types -- crocidolite, amosite, anthrophylite, tremolite, and actinolyte.

Amphiboles (particularly crocidolite) are considered to be more likely to cause cancer. However, the more commonly used chrysotile fibers are also linked with mesothelioma.

When chrysotile fibers in the air are inhaled, they tend to stick to mucus in the throat, trachea (windpipe), or bronchi (large breathing tubes of the lungs) and are then cleared by being coughed up or swallowed. But the long, thin amphibole fibers are less readily cleared, and they may reach the ends of the small airways and penetrate into the pleural lining of the lung and chest wall. These fibers may then injure mesothelial cells of the pleura, and eventually cause mesothelioma.

Asbestos fibers can also damage cells of the lung and result in asbestosis (formation of scar tissue in the lung) and/or lung cancer. Peritoneal mesothelioma, which forms in the abdomen, may result from coughing up and swallowing inhaled asbestos fibers. Because of its heat and fire resistant properties, asbestos was once used in many products such as insulation, floor tiles, door gaskets, soundproofing, roofing, patching compounds, fireproof gloves, ironing board covers, and brake pads. The link between asbestos and mesothelioma has become well known, so its use in the United States has decreased dramatically. Most use stopped after 1989, but it is still used in some products.

People at risk for workplace asbestos exposure include some miners, factory workers, insulation manufacturers and installers, railroad and automotive workers, ship builders, gas mask manufacturers, and construction workers. Family members of people exposed to asbestos at work also have an increased risk of developing mesothelioma because asbestos fibers can be carried home on the clothes of the workers. The incidence rate for mesothelioma in men appears to be dropping, probably because there is now much less direct exposure to asbestos in industrial workplaces.

Asbestos was also used in the insulation of many older homes, as well as commercial and public buildings around the country, including some schools.

The risk of developing mesothelioma is related to how much asbestos a person was exposed to and how long this exposure lasted. People exposed at an early age, for a long period of time, and at higher levels are more likely to develop this cancer.

Mesothelioma take a long time to develop. The time between first exposure to asbestos and diagnosis of mesothelioma is usually between 20 and 50 years. Unfortunately, the risk of mesothelioma does not drop with time after exposure to asbestos. The risk appears to be lifelong and undiminished.

2-Zeolites

Zeolites are silicate minerals that are chemically related to asbestos. An example is erionite, which is common in the soil in parts of Turkey. High mesothelioma rates in these areas are believed to be due to exposure to this mineral.

3-Radiation

There have been a few published reports of mesotheliomas that developed following exposure to high doses of radiation to the chest or abdomen or after injections of thorium dioxide (Thorotrast). This material was used by doctors for certain x-ray tests until the 1950s. Thorotrast was found to cause cancers, so it has not been used for many years.

4-SV40 virus

Some studies have raised the possibility that infection with simian virus 40 (SV40) might increase the risk of developing mesothelioma. Some injectable polio vaccines given between 1955 and 1963 were contaminated with SV40. As many as 30 million people in the United States may have been exposed to the virus. But up till now there is no conclusive evidence of increased cases of mesothelioma amongst people that have received this contaminated vaccine.