Asbestos and mesothelioma share an intertwined history, and for that reason the cancer known as mesothelioma is sometimes called an "asbestos cancer." Asbestos is the commercial--rather than scientific--term given to a naturally-occurring family of minerals that contain silicate and are found in rocks and dust in various parts of the world.

Asbestos was mined since the end of the 19th century for its strong, heat-resistant fibers. Although outlawed for most use in the U.S. in the 1970s due to the discovery that it was a major risk factor for diseases such as malignant mesothelioma and other respiratory diseases, asbestos was used during World War II and beyond, and can still be found in building products and fixtures such as:

• insulation
• roofing shingles
• paper products
• ceiling tiles
• cement products
• flooring felt
• gaskets
• millboard
• disc brake pads
• transmission parts
• textiles

Either in the mining, manufacturing, or removal process, asbestos fibers in the form of a fine dust tend to become airborne, particularly in dry environments. Airborne asbestos dust poses a serious risk of disease for workers or others who inhale or swallow it.

How asbestos causes mesothelioma remains a puzzle for researchers. But it is known that exposure to asbestos increases a person's risk of developing mesothelioma. Along with lung cancer and asbestosis (the development of scar tissue in the lungs), mesothelioma is one of the top three diseases associated with excessive asbestos exposure.

No longer mined, but still imported, asbestos continues to be used in some applications. Standards for what are acceptable levels of asbestos exposure were created by the U.S. Occupational Safety and Health Administration to help protect people from the harmful affects of asbestos.

Currently, .1 fiber per cubic centimeter is allowed - formerly, it was 5 fibers per milliliter. See the USOSHA site for the most current information on allowed standards for asbestos.

This Article Was Last Updated: October 17, 2009

According to the Environmental Protection Agency, asbestos comes in two main forms:

• chrysotile
• amphibole

Chrysotile fibers are curly and were used most often, while amphibole fibers are straight. Types of amphibole asbestos include:

• crocidolite
• amosite ("brown" asbestos)
• anthophyllite
• tremolite
• actinolite

The form of asbestos that has been demonstrated to be the most carcinogenic for mesothelioma is amphibole, possibly because their needle-like shape makes them more likely to attach to the body and not let go. Amphiboles were used extensively from the 1940s to the 1960s in the U.S. The chrysotile form was used most often.

The authors of Malignant Mesothelioma (Springer, 2005) state that knowing how much asbestos in a person's body is chrysotile vs. amphibole can help gauge the risk of developing mesothelioma. The issue can be complicated by the fact that chrysotile and amphibole are often both present in the same place, as in the case of tremolite, a form of amphibole, which contaminates the chrysotile in Canadian mines.

When naturally occurring, tremolite is also found in soils and rocks of Europe, Asia, Australia and the U.S. In Turkey, the culprit researchers attribute to causing local mesothelioma cases is zeolite.

Those who work with dry asbestos have a greater risk of developing malignant mesothelioma than those who work only in a wet asbestos environment, probably because the wet environment sends fewer asbestos particles airborne. The risk of mesothelioma induced by asbestos exposure is also affected by what exactly the work is, where it is conducted, when it was conducted, and how much time was spent doing it.

Researchers don't completely understand how asbestos causes mesothelioma. One hypothesis is that when sharp, tiny asbestos fibers penetrate cell walls in the pleural area, abdomen, or male internal reproductive organs, they damage the cells. In defense, the immune system creates an inflammatory response, sending mesothelial cells and macrophages to secrete substances that promote cellular replication of damaged cells rather than death--in other words, cancer. Part of the problem is the formation of scar tissue, or pleural plaque, whose presence can serve as evidence for the presence of asbestos.

This article is in no way meant to substitute for medical advice. If you are concerned about mesothelioma or any other health condition, talk to your doctor.