All types of asbestos fibers can cause serious health problems in people. The most common illnesses linked to long-term exposure to asbestos are asbestosis and mesothelioma.

Amosite and crocidolite are the most dangerous types of asbestos fibers. Chrysotile asbestos has also been shown to cause tumors in animals and is known to lead to asbestosis and malignant mesothelioma in humans. Mesothelioma has been found in people who worked with chrysotile, their family members, and people who lived near asbestos factories or mines.

In the 1980s and again in the 1990s, some people thought that making asbestos cement might make asbestos less harmful, either through chemical changes or by attaching cement to the fibers. However, later studies showed this was not true. Asbestos cement that was decades old, when broken, releases asbestos fibers that are the same as natural asbestos fibers, with no noticeable changes.

Risks

Exposure to asbestos in the form of fibers is always dangerous. Working with or being exposed to materials that are friable (easily broken apart) or that could release loose asbestos fibers is considered high risk. However, in general, people who become sick from inhaling asbestos are often those who have worked directly with the material in their jobs.

According to the National Cancer Institute, about 70% to 80% of all cases of illness caused by asbestos involve people who had a history of asbestos exposure at work. However, mesothelioma (a type of cancer) has also been reported in some individuals with no known asbestos exposure. A paper published in 1998 in the American Journal of Respiratory and Critical Care Medicine agrees, stating that asbestosis (a lung disease) is most often found in workers who handled asbestos and usually requires long-term exposure to high concentrations of the fibers to develop. The time between exposure and the appearance of illness, called the latency period, is typically 12 to 20 years, but can sometimes be as long as 40 years.

The most common diseases linked to long-term asbestos exposure are asbestosis and mesothelioma.

According to OSHA, there is no "safe" level of asbestos exposure for any type of asbestos fiber. Even brief exposure, such as a few days, has caused mesothelioma in some people. Every occupational exposure to asbestos increases the risk of developing an asbestos-related disease.

Diseases commonly associated with asbestos include:

• Asbestosis: Scarring of the lungs that worsens over time, leading to thickening and changes visible on X-rays. Symptoms may include abnormal lung sounds and wheezing. People exposed to asbestos through work, home, or environment should tell their doctors about this exposure.
• Asbestos warts: Growths on the skin caused by sharp asbestos fibers lodging in the skin and being covered by tissue.
• Pleural plaques: Thickened, sometimes calcified areas in the lungs visible on X-rays in people exposed to asbestos. These are not usually painful but may lead to thickening of the lung lining.
• Diffuse pleural thickening: Similar to pleural plaques, this condition may occur with asbestosis. It often has no symptoms but can cause lung problems with heavy exposure.
• Pneumothorax: Some studies have linked this condition (air in the space around the lungs) to asbestos-related diseases.
• Malignant mesothelioma: A serious, often deadly cancer that forms in the lining of the lungs (pleura) and is caused by asbestos exposure.

Safety and exposure prevention

Asbestos exposure becomes a problem when materials that contain asbestos become airborne, such as when they wear away or break. People who live in buildings may be exposed to asbestos, but those most likely to be affected are workers who intentionally disturb these materials, like maintenance or construction workers. Custodial workers, who may clean up damaged or worn asbestos materials without knowing they contain asbestos, may also be at higher risk. Workers who remove asbestos or emergency responders, such as firefighters, can also be exposed. People who live near asbestos mines or processing plants, or who are family members of workers, have been diagnosed with asbestos-related diseases.

In the United States, many products still contain asbestos today. In many parts of the world, especially the European Union, asbestos was removed from building materials starting in the 1970s, with most uses stopped by the 1980s. Even with a ban on asbestos, it can still be found in buildings built or renovated from the late 1800s to today.

Common asbestos-containing materials in homes include textured wall and ceiling materials, drywall joint filler, vermiculite mixed with asbestos, vinyl floor tiles, window putty, cement board, asbestos cement pipes, furnace tape, and stucco. Asbestos is also used in roofing materials, such as corrugated asbestos cement sheets and asbestos shingles. Other sources include fireproofing and sound-absorbing materials.

Asbestos fibers cannot be seen with the naked eye or identified using a regular microscope. Scientists use special tools like polarized light microscopy (PLM) or transmission electron microscopy (TEM) to find asbestos. PLM is cheaper, but TEM is more accurate and can detect smaller amounts of asbestos.

When asbestos is removed, workers check the job site visually and may test the air. Air samples are usually studied using phase contrast microscopy (PCM), which counts fibers on a filter. Rules for how much asbestos is safe to breathe are based on PCM results.

The American Conference of Governmental Industrial Hygienists suggests that no more than 0.1 asbestos fibers per milliliter of air should be inhaled over an 8-hour workday. In the United States and Canada, the same limit is used for safety.

Asbestos can be found naturally in outdoor air and in some drinking water. Even people who are not exposed to asbestos at work have thousands of asbestos fibers in their lungs. Naturally occurring asbestos (NOA) comes from rock deposits. Health risks from NOA are not fully understood, and federal rules in the U.S. do not address exposure from these deposits. Some areas, like parts of California and other states, have natural asbestos deposits near populated areas. Studies found that people who live closer to asbestos deposits are more likely to develop mesothelioma, a type of cancer, but not prostate cancer.

In El Dorado County, California, natural amphibole asbestos is found on the surface. A study by the U.S. Geological Survey found that some particles in the area meet rules for identifying asbestos but do not meet standards for commercial use. Experts noted that even non-commercial particles could be harmful and suggested more research. However, the study was criticized for testing areas without asbestos deposits and ignoring actual residential areas with asbestos. Because of this, no final results were published.

In Fairfax County, Virginia, tremolite asbestos is found under the ground. The county tested air at construction sites, controlled soil from affected areas, and required new sites to cover the ground with 6 inches of clean material.

Globally, ice in Antarctica shows chrysotile asbestos has been in the environment for at least 10,000 years. Snow samples in Japan show higher asbestos levels in cities than in rural areas. More asbestos fibers are found in urban areas where there are more asbestos-containing materials and activities that release fibers, such as braking in vehicles. Levels of 1–20 nanograms per cubic meter have been reported. Fibers longer than 5 micrometers are rarely found in rural areas. Studies using TEM have measured asbestos concentrations by mass.

Biological interactions

In 1977–78, Stanton and Layard suggested that the harmful effects of fibrous materials, like asbestos, are not caused by chemical reactions. Instead, they believed that physical effects, such as mechanical damage to cells, might be the cause. This damage could interfere with cell division, especially a process called mitosis.

Experiments have shown that very thin asbestos fibers (less than 60 nm in width, or 0.06 μm in thickness) can become tangled with chromosomes, which are similar in size. This tangling may lead to problems with mitosis, a process linked to cancer development.

Individual asbestos fibers are too small to see without special tools. They are about 3–20 μm wide and can be as thin as 0.01 μm. These fibers form when minerals cool and solidify. During this process, molecules line up in the same direction, creating crystal structures. These crystals have three weak points, called cleavage planes. When enough force is applied, the fibers tend to break along the weakest planes, creating long, thin shapes. This breaking process can repeat, causing one large fiber to split into many smaller ones.

When asbestos fibers or structures from materials containing asbestos become airborne, it is called primary release. Primary release can happen through processes like rubbing (abrasion), hitting (impaction), falling (fallout), wind erosion (air erosion), shaking (vibration), or fire damage. Secondary release occurs when settled asbestos fibers are lifted back into the air due to human activities. In buildings that are not occupied, fiber release usually happens through fallout or is caused by vibration or air erosion.

Friability refers to how easily a material containing asbestos can be broken. If a material is friable, it is very soft and weak, and can be crushed by simple finger pressure. Friable materials are a major concern because they are easily damaged. Most non-friable asbestos-containing materials are not broken by forces as small as finger pressure.

Smoking increases the risk of lung cancer in people exposed to asbestos. Studies have shown that people who smoke and are also exposed to asbestos have a higher risk of developing lung cancer compared to people who are exposed to asbestos but do not smoke.

History of health concerns and regulation

For more information in order of time, see also: List of asbestos disease medical articles.

Early concerns about the health effects of asbestos exposure in the modern era are found in several sources. In Britain, reports from the 1890s included a statement by Lucy Deane, who said asbestos had "easily demonstrated" health risks.

At about the same time, France reported what may have been the first study of deaths among asbestos workers. The study described the cause of death as chalicosis, a type of lung disease caused by dust. However, the conditions of the workers’ jobs suggested the real cause was exposure to asbestos or a mix of asbestos and cotton dust.

Awareness of asbestos-related diseases began in the early 1900s. In 1899, London doctor H. Montague Murray examined the lungs of a young asbestos factory worker who had died. During a legal hearing about worker compensation, Dr. Murray said the worker’s death was likely caused by breathing in asbestos dust.

In the United States, early observations about asbestos were based on stories and did not clearly connect the job to disease. Later, larger studies showed a stronger link. A study published in 1918 noted the dangers of asbestos exposure.

In 1924, British doctor Dr. Cooke described the case of a 33-year-old female asbestos worker, Nellie Kershaw, and noted that doctors in areas where asbestos was made had long suspected the dust caused lung problems. In 1927, Dr. Cooke reported on a 33-year-old male worker who was the only survivor of ten workers in an asbestos factory. He named the disease "asbestosis."

A large public health study in the late 1920s, now called the Merewether report, examined 360 asbestos-textile workers. It found that about 25% had lung disease. This led to better rules for making asbestos products in the 1930s, including safety standards, medical checkups, and including the asbestos industry in Britain’s Workers’ Compensation Act.

The first known U.S. workers’ compensation claim for asbestos disease was in 1927. In 1930, the first U.S. autopsy of a person with asbestosis was done, though the exposure happened in South America.

In 1930, the major asbestos company Johns-Manville created a report about deaths of asbestos workers for internal use. In 1932, the U.S. Bureau of Mines told a manufacturer that asbestos dust was one of the most dangerous types of dust for humans.

In 1933, doctors from Metropolitan Life Insurance Co. found that 29% of workers at a Johns-Manville plant had asbestosis. That same year, Johns-Manville settled lawsuits with 11 employees who had asbestosis, with the agreement that the employees’ lawyer would not sue the company again. In 1934, officials from two large asbestos companies changed an article about asbestos worker diseases to downplay the dangers. In 1935, these companies told the editor of Asbestos magazine not to write about asbestosis. In 1936, asbestos companies agreed to fund research on asbestos health effects but kept control over how the results were shared.

In 1942, a corporate memo from Owens-Corning mentioned many studies about asbestos dangers. In 1984, a former employee of Unarco described a meeting where a Johns-Manville official said it was cheaper to let workers with asbestosis die rather than pay for their care. In 1944, a Metropolitan Life Insurance Co. report found 42 cases of asbestosis among 195 asbestos miners.

In 1951, asbestos companies removed cancer-related information from research they sponsored. In 1952, Dr. Kenneth Smith, a Johns-Manville doctor, suggested adding warning labels to asbestos products, but the idea was not accepted. Smith later said the company avoided warnings because they feared losing money.

In 1953, a National Gypsum official wrote about the need for workers to wear masks when mixing asbestos-containing products. Another official said the letter was too risky and tried to stop it from being sent.

Through the 1970s, asbestos was used in fireproofing materials, insulation, and other products. It was also used in North Sea oil platforms and rigs.

During the mid-to-late 1980s, public health concerns focused on asbestos exposure in buildings and the risks of lung cancer or mesothelioma. The Health Effects Institute studied the cancer risks for building workers and occupants.

The United States is one of the few developed countries that has not completely banned asbestos. It is still allowed in some products, such as clothing, pipeline wraps, floor tiles, and roof coatings.

In 1989, the EPA tried to ban asbestos, but in 1991, a court ruled against the ban in a case called Corrosion Proof Fittings v. the Environmental Protection Agency. This decision allowed some products to still contain small amounts of asbestos. For more details on which products legally contain asbestos, see the EPA’s clarification statement.

Litigation

Asbestos-related lawsuits are among the largest legal cases in history because they lasted a long time, involved many people, and covered a wide range of issues. Several reasons explain this:

• Asbestos was used in many places: It was found in homes, buildings, fireproofing materials, and even decorative items like Artex. In some countries, more than half of homes had asbestos even after it was banned. This made asbestos very common.

• Health risks were known for a long time: People knew or suspected that asbestos caused health problems as early as the 1800s.

• The health effects were serious: Asbestos can cause deadly diseases, long-term care costs, loss of income, and other expensive compensation claims.

• Many people could be exposed: Diseases happen when tiny asbestos fibers are inhaled. This affected not only workers in industries like mining and construction but also people who handled asbestos products at home, in workplaces, or even those who washed clothes worn by workers.

• Diseases take years to develop: People often get sick decades after being exposed to asbestos.

• Companies may have hidden risks: Some asbestos businesses are accused of hiding or downplaying the dangers of asbestos.

In 1999, experts predicted that the number of people diagnosed with asbestos-related diseases worldwide would increase over the next 10 years. In the United States alone, the cost of asbestos lawsuits is estimated to be more than $250 billion.

In the United Kingdom, more people died from asbestos-related causes in 2011 (4,721) than from all traffic and transport accidents combined. That year, about 2,126 new cases were reported.

In the United States, asbestos lawsuits are the longest and most expensive mass legal cases in the country’s history. As of 2002, over 8,400 companies and 730,000 people were involved in these cases. At least one company had claims exceeding $800,000 in 2006.

The U.S. federal courts handled many asbestos-related cases, often involving multiple people with similar health issues. In 1999, 200,000 such cases were still being decided in federal courts. Experts estimate that the number of cases could rise to 700,000 over the next 40 years. These numbers explain why so many cases remain unresolved. Legal action involving asbestos has been slow, and some companies claim that workers are not currently sick or settle cases outside of court.

The large number of legal claims has worried manufacturers, insurance companies, and those who reinsure them. Disputes over how to pay compensation have led to many court battles and government efforts to resolve past and future cases.

In 1999, the United States considered but did not pass the Fairness in Asbestos Compensation Act. Since 1981, many asbestos companies have gone bankrupt, which limited how much money they could pay to people affected by asbestos. Christopher Edley, Jr. said that if the 1999 law had passed, it would have limited punishments for actions taken by company leaders long ago.

Asbestos lawsuits also happen in other countries, including England, Scotland, Ireland, the Netherlands, France, Italy, and Japan. However, the amounts paid in these countries are usually smaller than in the United States. For more details, see the related article.

In Australia, a major and controversial case was brought against James Hardie, a company that mined and sold asbestos-related products for many years.

Criticisms of asbestos regulation

Criticisms of regulations include a claim by Dixy Lee Ray that the Space Shuttle Challenger broke apart because the company that made O-ring putty was forced by the EPA to stop making putty containing asbestos. However, the putty used in Challenger's last flight did contain asbestos, and the failure of the O-ring that caused the disaster was not due to the putty.

Asbestos was also used in the first forty floors of the World Trade Center's north tower. After the towers fell during the September 11 attacks, asbestos particles spread into the air in lower Manhattan. A later claim by Steven Milloy of the Cato Institute suggested that if a 1971 ban on asbestos had not stopped the completion of asbestos coating above the 64th floor, the towers might have remained standing longer. This idea was not included in the National Institute of Standards and Technology's report on the towers' collapse. The report explained that all fireproofing materials must meet fire-resistance standards before being used, and all lightweight spray fireproofing materials, including those with asbestos, are not tested for damage caused by high-speed impacts. Therefore, using asbestos as fireproofing would not have prevented the towers from collapsing. When the towers fell, any asbestos present would have been widely scattered into the air by the large dust cloud.