Exposure to asbestos is unlikely to cause any short term (acute) effects beyond irritation of the nose or throat. It is the long-term (chronic) effects that are debilitating and deadly. Every kind of asbestos causes cancer, and every kind of asbestos can cause asbestosis. People are exposed to asbestos mainly through inhalation of fibers in the air they breathe. This may occur during mining and processing of asbestos, during the production of asbestos-containing products, or during the installation of asbestos insulation. It may also occur when older asbestos-containing materials begin to break down. In any of these situations, asbestos fibers tend to create a dust composed of tiny particles that can float in the air. In addition, asbestos can enter the body through ingestion. This may occur when people consume contaminated food or liquids (such as water that flows through asbestos cement pipes). It may also occur when people cough up asbestos they have inhaled, then swallow their saliva. Many people are exposed to very low levels of naturally occurring asbestos in outdoor air as a result of erosion of asbestos-bearing rocks. Family members of asbestos workers are also potentially exposed to higher levels of asbestos because the fibers are carried home on the workers’ clothing, and can then be inhaled by others in the household. Inhalation of asbestos fibers has been proven to cause lung cancer.
The most common way for asbestos fibers to enter the body is through breathing. In fact, asbestos containing material is not generally considered to be harmful unless it is releasing dust or fibers into the air where they can be inhaled or ingested. Many of the fibers will become trapped in the mucous membranes of the nose and throat where they can then be removed, but some may pass deep into the lungs, or, if swallowed, into the digestive tract. Once they are trapped in the body, the fibers can cause health problems. The most serious hazard of exposure to asbestos is cancer, and it takes less exposure to asbestos to cause cancer than to cause asbestosis. Two kinds of cancer are very strongly related to asbestos: lung cancer and mesothelioma. In addition, asbestos also causes cancer of the throat, stomach, esophagus, and bowel. Lung cancer caused by asbestos exposure is the same kind of cancer as that caused by smoking. It is hard to diagnose early, it spreads rapidly, and can rarely be cured.
Lung cancer in asbestos-exposed and unexposed individuals is similar in both the type of cancer and its signs and symptoms. The link between cigarette smoking, asbestos and cancer of the lung itself does not apply to cancer of the lining of the lung (see malignant mesothelioma section below). Diagnosis and treatment of lung cancer is a complex topic and a pulmonary specialist should be involved in the workup of a suspected lung cancer. Exposure to asbestos fibers, either at home or in the workplace, is also considered a risk factor for lung cancer. Studies show that compared to the general population, asbestos workers are seven times more likely to die from lung cancer. Asbestos workers who smoke increase their risk of getting lung cancer by 50-100 times. The risk of asbestos-related abnormalities and disease generally increases with increasing levels of exposure. This dose-response relationship is less clear for mesothelioma, where even short-term occupational exposures or secondary household exposures (e.g., household contacts of asbestos workers) have been associated with the occurrence of this malignancy. As asbestos exposures have declined in the workplace due to regulatory control, cases of severe interstitial disease have also decreased. Mesothelioma is a fast spreading cancer that is almost always caused by exposure to asbestos. It can take 30 or 40 years after exposure to develop. Mesothelioma usually starts in the membrane that wraps around the lungs, called the pleura. The cancer cells cause a build-up of fluid between the pleura and the lungs, which in turn causes pressure on the lungs. The symptoms are shortness of breath and a dry, painful cough. The cancer may eventually grow into the chest wall. Sometimes, the cancer can develop in the lining of the abdomen, the membranes of the heart or reproductive organs. Among many recently screened cohorts, pleural changes are more prevalent than interstitial changes. There is little evidence that general environmental exposures are associated with significant disease except in several regions of the world with endemic mesothelioma due to exposures from naturally-occurring deposits of asbestos.
Lung cancer causes the largest number of deaths related to asbestos exposure. The incidence of lung cancer in people who are directly involved in the mining, milling, manufacturing and use of asbestos and its products is much higher than in the general population. The most common symptoms of lung cancer are coughing and a change in breathing. Other symptoms include shortness of breath, persistent chest pains, hoarseness, and anemia. The association between lung cancer and asbestos exposure is now well established. In the case of smokers who have had significant asbestos exposure, the risk of lung cancer is extraordinarily high. Lung cancer in asbestos exposed workers is thought to occur at a slightly earlier age than other lung cancers and are more common in the lower lobes.