What is asbestos? Does it cause cancer?

Exposure routes: Inhalation and ingestion

Where found: Materials for roofing, thermal and electrical insulation, cement pipe and sheets, flooring, gaskets, friction materials, coatings, plastics, textiles, paper, and other products

At risk: Workers in asbestos mining and milling, shipyards, building demolition, insulation, brake repair, and asbestos abatement, and their families

Etiology and symptoms of associated cancers: Several asbestos-related conditions are nonmalignant, including asbestos warts (callus-like growths that form when asbestos fibers become embedded in the skin), asbestosis, pleural plaques, pleural thickening, and pleural effusions (the collection of fluid around the lung a few years after asbestos exposure). Inhaled or ingested asbestos fibers lead to the two most serious asbestos-related disorders: the noncancerous asbestosis, in which scarred and increasingly stiff lung tissue progressively reduces breathing capacity, and the cancer known as malignant mesothelioma. These diseases may take years or decades to develop, although there have been cases of adolescents developing mesothelioma within only a few months of initial asbestos exposure.

Malignant mesothelioma takes two main forms: pleural mesothelioma, in which tumors form on the outer lining of the lungs, and peritoneal mesothelioma, in which tumors form on the peritoneum, the sac containing the abdominal organs. The rarer forms of malignant mesothelioma are pericardial mesotheliomas and mesotheliomas of the tunica vaginalis, affecting the heart and testicles, respectively. Malignant mesothelioma has a low survival rate—in 2014 it was only 5 to 10 percent after five years, according to the American Society of Clinical Oncology—because it is rarely detected in its early stages. The American Cancer Society reported in 2013 that as many as fifty years can pass between first exposure to asbestos and a mesothelioma diagnosis and that about 67 percent of mesothelioma patients are aged sixty-five or older. Symptoms including chest pain, cough, weight loss, and shortness of breath are often attributed to more common diseases such as asthma. As the cancer spreads, lung capacity is diminished, and the patient eventually succumbs to the inability to take in sufficient oxygen, if not to the failure of other organs after the cancer metastasizes.

Asbestos exposure has also been associated with cancers of the stomach, liver, and other organs. Researchers have observed digestive-tract cancers in workers exposed to crocidolite, amosite, and chrysotile, although study results are inconsistent. An excess of laryngeal cancer has been reported in shipyard workers, chrysotile miners, insulation workers, and others exposed to asbestos. People living near asbestos factories or mines or living with asbestos workers have also developed mesothelioma; however, there is no clear association between cancer risk and exposure to asbestos in drinking water. Smokers who are also exposed to asbestos are at a synergistically (rather than additively) greater risk of developing lung cancer.

History: In the 1930s, researchers established that asbestos presented especially high risks of causing lung diseases in miners, shipyard workers, and others who either manufactured or worked with materials incorporating asbestos, such as insulation. It soon became evident that exposure to minute amounts of asbestos could lead to asbestos-related disorders. Miners’ spouses developed mesothelioma after being exposed to asbestos through doing laundry, for example, while children became victims through exposure to their parents’ work clothes in the home.

In the United States, asbestos was one of the first hazardous air pollutants regulated by the Clean Air Act of 1970. The first lawsuits resulting from occupational exposures began in the late 1960s and increased in 1973 when the Fifth Circuit Court of Appeals applied strict liability in Borel v. Fibreboard Paper Prods. Corp. (493 F.2d 1076). In 1976, Congress passed the Toxic Substances Control Act, which imposed regulations regarding asbestos, including a requirement that asbestos abatement occur in schools. The International Labour Organization’s Asbestos Convention of 1986 mandated that national laws should “prescribe the measures to be taken for the prevention and control of, and protection of workers against, health hazards due to occupational exposure to asbestos.”

The widespread use of asbestos fibers in multiple applications means that exposure remains a concern in the twenty-first century. Although asbestos is no longer as widely used in industry, which has reduced exposure in the workplace, people still risk asbestos exposure when engaging in home improvement projects as they rip out old flooring or replace ceiling tiles.

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