Causes of Mesothelioma

Exposure to asbestos is the only known cause of mesothelioma. Inhaling or ingesting asbestos causes these microscopic fibers to get lodged in the lining of the chest or abdomen. Over time, the fibers cause tumor development because the body is incapable of expelling the fibers.

Asbestos is a naturally occurring mineral used for centuries in products ranging from textiles to insulation. Asbestos usage increased throughout the world in the first half of the 20th century and peaked in the United States during World War II. Asbestos continued to be used in a wide variety of industries until the 1980’s. To date, roughly 30 million tons have been used in the United States alone.

There are several ways people are exposed to asbestos.

Types of Asbestos Exposure

Occupational: Some people were directly exposed to asbestos at their jobs. Asbestos products were widely used in construction and industrial trades. This is called occupational, or first-hand, exposure.

Secondhand: Other people were exposed to asbestos found on the clothes of someone working with or near the mineral. This is known as secondhand exposure.

Environmental: As a mineral, asbestos can be found in nature. Traditionally, asbestos mines that operated in the past released fibers into the air.

Asbestos: A Cancer-Causing Mineral

Asbestos is made up of flexible, microscopic fibers that are lighter than air and have high tensile strength. Each fiber is hundreds of times thinner than the average human hair. Asbestos is also highly resistant to heat, water, and corrosive damage. These natural properties made asbestos an ideal material for a variety of applications ranging from building insulation to gaskets to brake pads in cars.

There are two main categories of asbestos: serpentine and amphibole.

These categories are characterized according to the shape of the asbestos fibers.

Serpentine: These wavy fibers are found in approximately 95 percent of commercially developed asbestos products in the United States. Because of their shape, serpentine fibers are more easy to breath out from the body than amphibole fibers.

Amphibole: These spindle-shaped fibers are sharp, rigid, and more capable of lodging themselves in body tissue. This characteristic increases the risk of developing mesothelioma.

There are six types of asbestos, two of which (actinolite and tremolite) are not commercially used. The four types that can be found in a wide range of materials and products are:


  • White
  • Only form of serpentine asbestos
  • Accounts for the vast majority of asbestos used commercially
  • Curled fibers
  • Chrysotile fibers are more easily removed from the body than other forms of asbestos

Crocidolite and Amosite:

  • Crocidolite is blue in appearance while amosite is brown
  • Used on ships and spray-on insulation products
  • Both form a brittle, needle-like structure, whose fibers are difficult to dislodge from the respiratory tract


  • Gray
  • Used in a variety of commercial applications

Asbestos and Mesothelioma

Asbestos is not an automatic threat. Before it can do damage to your body, asbestos must be inhaled or ingested. Organizations, such as the Environmental Health Agency (EPA), do not acknowledge any safe level of asbestos exposure.

Asbestos is categorized as a carcinogen by the following health organizations:

  • US Department of Health and Services
  • EPA
  • International Agency for Research on Cancer

Generally speaking, asbestos enters the body as follows:

  • Microscopic asbestos fibers are inhaled and travel through the airways
  • After inhalation, roughly two-thirds of the fibers are breathed out from the body. Some fibers remain and become lodged in the lining of the lungs (the pleura), abdominal cavity (the peritoneum) or heart (pericardium)
  • Over time, the tiny fibers cause scarring, inflammation, and genetic changes that develop into mesothelioma

Current Theories Linking Asbestos Fibers and Tumor Growth

Research has not yet shown how exactly mesothelioma causes the genetic changes leading to the development of a tumor. There are a number of theories concerning this process, such as:

  • The microscopic size and needle-like shape of asbestos could prevent cells in the immune system from clearing the fibers out. Cells in the mesothelial lining then absorb the fibers, which in turn interfere with normal cellular division.
  • Inhaled fibers irritate mesothelial cells, causing them to swell. This results in cellular damage and tumor development.
  • Asbestos fibers may influence the production of molecules that damage DNA and disrupt cellular reproduction. This damage leads to the production of tumors.
  • Asbestos fibers may also influence the production of proteins that can mutate regular mesothelial cells into tumor cells.

Regardless of how asbestos fibers cause mesothelioma, symptoms do not usually present themselves until 10 to 50 years after the initial exposure to asbestos occurred. Mesothelioma symptoms are often mistaken for those of other ailments.

You can learn more about the causes of mesothelioma and how this disease is treated in our free Patient Help Guide.

Types of Asbestos Exposure

Exposure to asbestos can occur in a number of ways. The three most common methods that people come into contact with asbestos are at work (occupational), in the military and at home through secondhand exposure. In very rare cases, some people are exposed to asbestos in nature.

Occupational Exposure

The most common type of asbestos exposure occurs at work. About 70 to 80 percent of all mesothelioma cases are work-related. Workers dealing directly with the manufacture and installation of asbestos-containing products, such as insulation, have the highest risk of developing mesothelioma. Manufacturers stopped mass producing asbestos products in the 1970s and 80s, so workers today have less risk. However, people exposed to asbestos in the 70s and 80s may still be at risk because it takes up to 50 years for mesothelioma to develop after exposure.

Many large companies who knowingly exposed their employees to asbestos have set up asbestos trust funds to help victims pay for treatment.

Occupations presenting the most risk for asbestos exposure are:

  • Drywall installers
  • Demolition specialists
  • Firefighters
  • Mill workers
  • Power and chemical plant operators
  • Automobile and airplane mechanics
  • Shipbuilders

Veterans. All branches of the military used asbestos-containing materials between the 1930s and 1970s. As a result, veterans are the group most at risk for developing mesothelioma. They account for nearly a third of all mesothelioma diagnoses.

Secondary Exposure

Mesothelioma can also develop in people who have not worked directly with asbestos-containing materials. Asbestos workers would often unknowingly expose their families to asbestos after work. Family members were exposed via clothes coated with dust containing tiny asbestos fibers. The slightest movement released fibers into the air, increasing each family member’s risk of developing mesothelioma. Unfortunately, few people knew the risks related to asbestos until the 1980s.

Survivor Profile: Louise Williams

Louise was first diagnosed with peritoneal mesothelioma in 2003 and again in 2009 with pleural mesothelioma.

She attributes her diagnoses to the frequent secondary asbestos exposure she endured as a child. Her father worked with asbestos and would unknowingly expose her and her siblings to asbestos dust on his work clothes.

Environmental Exposure

Asbestos is a naturally-occurring mineral, and people had to mine it to make asbestos-containing products. Environmental exposure to asbestos often occurs near mines that produce or process asbestos. The daily operation of these mines may have released microscopic fibers into surrounding area. In the past, airborne asbestos fibers could float into nearby communities.

Asbestos is a mineral that gathers natural deposits, some of which occur very near the surface. When these deposits are disturbed, they can release fibers into the air, contaminating the surrounding area. Sometimes asbestos deposits are disturbed by cars or trucks.

Mesothelioma Risk Factors

Asbestos exposure is far and away the main cause of mesothelioma. There are factors, however, that may increase the risk of developing mesothelioma. Some of these factors may even cause mesothelioma without exposure to asbestos.

Age: Older people are more likely to be diagnosed with mesothelioma due to the amount of time symptoms associated with the disease take to appear. Two out of three people diagnosed with mesothelioma are older than 65.

Gender: Mesothelioma is more common in men than women. Though research has not determined the exact reason why, the increased risk may be connected to the type of labor traditionally occupied by men. These jobs are most likely to involve exposure to asbestos.

SV40 (Simian Virus 40): In 1961, polio vaccines were found to be contaminated with SV40, a virus known to affect monkeys and apes. Sixty-two percent of the American population had been treated with the contaminated vaccine before SV40 was removed.

Erionite: Erionite is a naturally occurring fiber linked to the development of mesothelioma. It shares physical characteristics with crocidolite, a subtype of asbestos. Erionite was used heavily in Cappadocia, Turkey as a construction material.

Studies of death rates in Cappadocia showed that 24 percent of the deaths that occurred over a period of 4 years were a result of mesothelioma. These deaths have been linked by researchers, most famously by mesothelioma specialist Dr. Michele Carbone, to extensive erionite exposure.

Vermiculite: Vermiculite a naturally occurring mineral that can be contaminated by asbestos.

Genetic Predisposition: A study performed on a group of unrelated families showed that mesothelioma may have a genetic component. The presence of an inherited mutation in BAP1, a gene that inhibits tumor development, was linked to the increased incidence of mesothelioma.

Taconite: Taconite is a sedimentary rock used in the manufacture of steel products. It has been linked to a number of mesothelioma diagnoses.

Radiation Exposure: Ionizing radiation is often used to treat cancer. A few studies have linked this treatment to the development of mesothelioma.

Chronic Inflammation: Researchers have proposed that chronic inflammation may play a role in the development of cancer. The presence of recurring inflammation may make the body more susceptible to the growth of malignant tumors.

Taking Action

If you or a loved one have been exposed to asbestos, it is important to visit a doctor for a check up. Symptoms of mesothelioma can take decades to appear after the initial exposure to asbestos occurred. Those experiencing symptoms should seek help from a mesothelioma specialist as soon as possible.


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