Exposure to asbestos fibers is the only proven cause of pleural and peritoneal mesothelioma. Patients are most often exposed to asbestos in occupational settings.

What Causes Mesothelioma?

Asbestos exposure is the only proven cause of mesothelioma. Asbestos is a naturally occurring mineral, originally admired for its unique insulating and fire retardant capabilities.

How Do People Get Exposed to Asbestos?

  • Occupationally

    Occupational exposure is the most common type of exposure. Those working in industrial occupations frequently worked with materials containing asbestos. Electricians and shipyard workers were among those most commonly exposed to asbestos on the job.

  • Secondhand

    Secondhand exposure occurred when those working in occupations using asbestos materials would inadvertently expose people at home. Asbestos in hair and on clothes was transferred to others not directly working with toxic materials.

  • Naturally

    Asbestos is a naturally occurring mineral. Those who lived near large deposits of asbestos may have been exposed through water run-off or mining projects. This form of exposure is rare.

What is Asbestos?

Asbestos is a naturally occurring mineral found in rock and other minerals, such as vermiculite. There are two main types of asbestos: serpentine and amphibole. Serpentine asbestos is generally less friable than amphibole asbestos.

These categories of asbestos are further broken down into subcategories, but they are all tiny, thin fibers that make up the mineral. The average human hair is approximately 1,200 times thicker than an asbestos fiber.

There are different types of asbestos:

  • Serpentine asbestos – These wavy white fibers are able to be expelled by the body and therefore the least threatening. Serpentine asbestos fibers make up 95% of all asbestos found in building in the United States (subtypes: chrysotile)
  • Amphibole asbestos – The body has a much harder time removing these fibers as they are rigid and needle-like. They can become lodged in the body and are the most deadly. (subtypes: amosite, tremolite, actinolite, anthphylite, and crocidolite)

How Does Mesothelioma Develop?

Exposure to asbestos is most likely to occur when materials containing asbestos are disturbed or loosened, releasing asbestos fibers into the air. Mesothelioma develops when:

  • 1
    Airborne microscopic asbestos fibers are inhaled or ingested.
  • 2
    The body attempts to remove these fibers but instead they become stuck in the protective lining surrounding the lungs, abdomen, or heart.
  • 3
    The trapped fibers irritate the mesothelial cells, causing genetic mutations that develop into tumors over time.

These genetic mutations affect cell division and cause mesothelioma tumors. Mesothelioma may take between 20-50 years to show symptoms. Symptoms are often mistaken as a common cold or pneumonia with chest pain, breathing discomfort, or a consistent cough.

Men are more commonly diagnosed with mesothelioma than women at a ratio of 5 to 1. This is most likely because men have traditionally worked industrial jobs where asbestos was prevalent. Learn more about occupational asbestos exposure and how it causes mesothelioma in our free Mesothelioma Guide.


The cause of mesothelioma is generally attributed to asbestos exposure, but determining when the exposure occurred can be difficult. In some cases, patients may not even realize they have been exposed to asbestos at all.

Exposure can occur in unlikely places, including the household. However, when left undisturbed, most materials containing asbestos pose no immediate threat.

Home insulation manufactured before 1975 contains asbestos, as well as many other building materials found in homes.

Remodeling work on older homes poses the risk of releasing asbestos fibers into the air by disturbing asbestos-containing building materials. Asbestos is not only found in homes, but also in cars. Brake pads, clutches, gaskets and insulation material can contain asbestos, especially in older cars.

The Environmental Protection Agency began requesting lists from American companies of their products containing asbestos in 1981, which eventually led to the Asbestos Information Act of 1988. Although asbestos is still used in the United States, this law requires manufacturers of asbestos products to submit detailed information on their products to the EPA.


Regulations regarding asbestos also categorize different types of asbestos into friable and non-friable asbestos. Friability is simply how easily a substance crumbles or breaks apart. Non-friable asbestos-containing materials are generally considered as relatively safe (when undisturbed). However, friable asbestos-containing materials are much more dangerous. non-friable asbestos-containing materials are regulated in the United States; however, any asbestos-containing material can become friable.

Occupational Exposure

Occupational hazards are the most common cause of asbestos exposure. People employed in shipyards, automotive jobs and the military have an especially high risk of developing mesothelioma. These people are at a higher risk of asbestos exposure because of the materials they worked with.

Some common industrial materials containing asbestos are:

  • Insulation
  • Roofing and flooring materials
  • Brake pads
  • Pipes and pipe fittings
  • Electrical wiring
  • Paint

Asbestos production increased substantially during World War II. The increased production of ships, aircraft and other vehicles was a major reason why asbestos became so commonly used. Its insulation and fire resistance properties made asbestos a convenient material for most industrial applications. This put military veterans and those in industrial occupations at risk.

The companies responsible for the increased use of asbestos containing materials knew about the risks associated with asbestos. Many of these companies have filed bankruptcy and set up trust funds to handle the claims against them. If you are a victim of occupational exposure, you may be entitled to compensation from one or more of these asbestos trust funds.

Secondary Exposure

Some mesothelioma victims do not remember where they were exposed. Others may not even realize they were exposed. It is possible these individuals had secondhand exposure to asbestos.

Spouses of construction or factory workers are the most common example of secondary exposure. Many workers returned home with asbestos fibers on their clothes, skin, and in their hair. Secondary exposure occurred from contact with the directly-exposed spouse and even from doing laundry.

Secondary asbestos exposure has occurred in occupational environments as well. Any workers who spent time around employees exposed to asbestos could be at risk.

Lastly, secondary asbestos exposure has occurred in communities where asbestos was released into the air from nearby factories manufacturing asbestos materials, shipyards, mills, mines, and building demolitions.

Libby, Montana

Libby, Montana is an example of mining leading to secondary exposure. W.R. Grace and Company took over the vermiculite ore mine in Libby in 1963. Despite knowing the dangers of asbestos, the mine operated without regulations until 1990. The EPA has spent over $450 million on the cleanup, and at least 300 deaths have been attributed to this one location. The Affordable Care Act offers financial assistance for mesothelioma victims and public health emergencies like Libby.

Naturally Occurring Exposure

Some people may come into contact with naturally occurring asbestos fibers. This classification of asbestos refers to the naturally occurring minerals found in underground rock, which is mined and used in commercial building materials.

Most naturally occurring asbestos is too deep underground to be easily disturbed. However, there are some areas where naturally occurring asbestos is close enough to the surface to pose a threat to people in the immediate vicinity. There is also a significant threat of occupational exposure to naturally occurring asbestos for miners.

Although rare, there is potential for water contamination from run-off of land erosion. When it rains, the naturally occurring asbestos has the potential to contaminate natural water supplies like rivers or lakes. This happens when dirt is pushed down a mountain or hillside by the rain.

One instance of water contamination was in Coalinga, California. The Coalinga Asbestos Mine covers over 120 acres and has contaminated the water supply through mining activities.

Risk Factors

There are several risk factors that account for the development of mesothelioma and can increase the risk of cancer. The basic factors which increase the risk of developing mesothelioma are:

  • Occupation
  • Type of Asbestos
  • Exposure Duration/Frequency
  • Previous Lung Disease
  • Working Conditions
  • Breathing Rate While Exposed
  • Weather
  • Exposure Concentration

One of the most prominent factors involved in asbestos exposure is work history. Today, occupational exposure does not pose the same threat it did before the 1980s due to standards of permissible exposure limits and other regulations. However, this risk is higher if working conditions did not meet these standards.

Before the 1980s, working conditions with respect to asbestos exposure varied depending on the specific profession. Miners, for example, were likely to be exposed to higher concentrations of asbestos because of the poorly ventilated working conditions.

The breathing rate of the worker during exposure is another factor closely related to concentration. More fibers are likely to be inhaled with a higher breathing rate. Weather during the time of exposure is also a factor because rainy weather lowers the particulate count of fibers in the air. Therefore, dry weather during exposure increases the risk of developing mesothelioma.


People who are most at risk for mesothelioma include: men, those over 65 years of age and military veterans. Over 75 percent of people who die from mesothelioma are men. This makes sense as most asbestos exposure occurred in construction related occupations historically dominated by men.

Mesothelioma symptoms usually appear in patients between the ages of 50 and 70 years old. However, they can occur in patients as early as their 20’s if they were exposed at a young age. There are also certain states where instances of mesothelioma are more common.

Veterans and Mesothelioma

Historically, veterans have been exposed to asbestos more than any other group. Over one-third of mesothelioma patients have served in the military, mostly in the Navy.

Because it wasn’t widely known that asbestos was harmful until the 1970s and 80s, it was used in hundreds of applications in the military—from insulating engine rooms in naval vessels to insulation in barracks. Many veterans who worked as shipbuilders, electricians and steelworkers developed mesothelioma from occupational exposure during their service.

Smoking and Mesothelioma

Cigarette smoke contains numerous carcinogens that can cause cancer. However, a direct relationship between smoking and mesothelioma is unlikely according to current research. In other words, smoking doesn’t increase your chances of developing mesothelioma.

This doesn’t mean it’s okay to smoke. Smoking decreases a patient’s overall health which is an important prognostic factor. Furthermore, smoking combined with asbestos exposure has shown to significantly increase the likelihood of developing lung cancer. The carcinogenic materials in cigarette smoke and asbestos fibers work together to create cancerous tumors.

How Do I Take Action?

Those who believe they have been exposed to asbestos should be aware of the symptoms associated with asbestos related diseases. These may be harder to detect when they occur in people with chronic breathing issues like asthma, so staying conscious and aware of your health is key. Individuals who have been exposed to asbestos should consider seeing a physician who can test for any abnormalities.

If you have been diagnosed with mesothelioma, the first course of action is to find a specialist who can treat you and improve your prognosis.

The second course of action is to find all means of support to get you through your diagnosis. There are several avenues of compensation for mesothelioma patients to help pay for treatment and other expenditures.