Causes of mesothelioma

Up to 9 out of 10 cases of mesothelioma are caused by exposure to asbestos. Asbestos is a natural mineral, mined from rock found in many countries. It is made up of tiny fibres that are as strong as steel but can be woven like cotton and are highly resistant to heat and chemicals.

Before the 1980s, asbestos was imported to the UK in large quantities. It was used in construction, ship-building and in household appliances. When asbestos is disturbed or damaged, it releases tiny fibres that can be breathed into the lungs and cause inflammation, a build-up of scar tissue (fibrosis) and sometimes cancer.

During the 1960s the first definite link between mesothelioma and asbestos was made. Asbestos is now known to be the most common cause of the disease.

Asbestos was very widely used in insulation materials, such as amosite insulation board, and building materials, including asbestos cement. Asbestos fibres are very fine and if they are breathed in they can make their way into the smallest airways of the lung, so they cannot be breathed or coughed out. Once the fibres are in the lungs the body’s defence mechanism tries to break them down and remove them, which leads to inflammation in the lung tissue.

The asbestos fibres can also penetrate through the lung tissue to settle in the pleura (the membrane around the lung). Over many years they can cause mesothelioma or other lung diseases to develop.

The asbestos fibres can also be swallowed, and some of the fibres can stick in the digestive system. They can then move into the membrane that lines the abdomen (the peritoneum), where they cause inflammation.

The people likely to have been exposed to asbestos include:

• construction workers
• plumbers
• electricians
• boilermakers
• shipbuilders
• demolition workers
• people who lived near to asbestos factories
• people who worked in places where asbestos was present.

Family members of people who worked with asbestos and brought the dust home on their clothes have sometimes developed mesothelioma.

There are three types of asbestos: blue, brown and white. Blue and brown asbestos, are most commonly linked with mesothelioma. They are now very rarely used and cannot be imported into the UK. Originally, white asbestos was not thought to be dangerous but recent studies have now shown that it is also harmful.

Mesothelioma does not usually develop until 10–60 years after exposure to asbestos and for this reason it is often difficult to discover the exact cause.

In the 1980s, imports of blue and brown asbestos into the UK were stopped and in 1999 the importation and use of all asbestos was banned. However, as mesothelioma develops so slowly, it is estimated that by 2015 approximately 3000 people will be diagnosed with mesothelioma each year. The number of people who develop mesothelioma will then start to reduce each year.

Occasionally, mesothelioma develops in people who have never been exposed to asbestos. The other causes of the disease are not fully understood, but in rare cases the development of mesothelioma has been linked to exposure to radiation.

Currently a research study is taking place to try to find out more about the causes of mesothelioma. It is called the National Study of Occupation and Lung Diseases. Your doctor may invite you to take part in the study, and if you agree you will be asked to fill in a short questionnaire and have a telephone discussion for about an hour with a researcher.

Research has not found any evidence that smoking increases a person’s risk of developing mesothelioma. It is also thought that exposure to other building materials such as fibreglass does not increase the risk.

Mesothelioma is not contagious and cannot be passed on to other people. It is not caused by inherited faulty genes and so family members do not have an increased risk of developing it, unless they have been in contact with asbestos.