Asbestosis

The incidence of asbestosis varies with the cumulative dose of inhaled fibers; the greater the cumulative dose, the higher the incidence of asbestosis. The risk of developing asbestosis after a cumulative dose of 10 fiber-year/m³ has been estimated at approximately 1%. ^[5]

All types of asbestos fibers are fibrogenic to the lungs. Amphiboles, particularly crocidolite fibers, are markedly more carcinogenic to the pleura. ^[5]  The dimensions of the fibers are also important. ^{[6, 7]} Fibers with diameters smaller than 3 μm are fibrogenic because they penetrate cell membranes. Long fibers (ie, >5 μm) are incompletely phagocytosed and stay in the lungs, leading to cytokine release and cell destruction.

The initial inflammation of asbestosis occurs in the alveolar bifurcations, characterized by the influx of alveolar macrophages. Asbestos-activated macrophages produce a variety of growth factors, including fibronectin, platelet-derived growth factor (PDGF), insulinlike growth factor (IGF), and fibroblast growth factor (FGF), which interact to induce fibroblast proliferation.

Reactive oxygen species (ROS; eg, superoxide anion, hydrogen peroxide, and hydroxy radicals) released by the macrophages damage proteins and lipid membranes, potentiating the inflammatory process. A plasminogen activator, which is also released by macrophages, further damages the interstitium of the lung by degrading matrix glycoproteins.

Individuals probably vary in their susceptibility to asbestosis on the basis of differences in respiratory clearance and other unidentified host factors. People who smoke have an increased rate of asbestosis progression, likely due to impaired mucociliary clearance of asbestos fibers. ^[8]  In addition, although the data regarding the association between MUC5B promoter polymorphism and idiopathic pulmonary fibrosis (IPF) appear to be clear, the data regarding whether the MUC5B promoter variant is a potential genetic risk factor for asbestosis have been mixed. ^{[9, 10, 11]}

Uncertainty remains about the mode(s) of action of asbestos in the genesis of diseases; in an effort to reduce this uncertainty, an expert group has proposed cooperative action by diverse scientific disciplines to address such issues as terminology, mineralogy, test materials, and experimental models. ^[12]

Antinuclear antibodies

Exposure to amphibole asbestos fibers is linked to autoantibody production. Studies have indicated that asbestos-related abnormalities occur more often in individuals who test positive for antinuclear antibodies (ANAs) than in those who test negative. ^[13] These studies were conducted in Libby, Montana, where mining, transportation, and processing of asbestos-contaminated vermiculite caused an increased risk of asbestos-related pleural and lung diseases. Serum samples showed that most of the people sampled were ANA-positive. ^{[14, 15]} In addition, the risk of developing pleural or interstitial abnormalities was more than three times higher in ANA-positive individuals than in ANA-negative individuals. ^[14]

Despite the association with ANA seropositivity, there is no clear link between asbestos exposure and the development of autoimmune disorders such as systemic lupus erythematosus. This lack of association with autoimmune disease is in stark contrast to silicate dust exposure, for which there is a clear association with the development of autoimmune disorders. ^{[16, 17, 18]}

Sources of asbestos exposure

As noted earlier, exposure to asbestos occurs through inhalation of fibers in air in the working environment, ambient air in the vicinity of factories handling asbestos, or indoor air in housing and buildings containing asbestos materials. Asbestos has commonly been used in the following products:

• Products containing asbestos cement ^[19] - Pipes, shingles, clapboards, sheets
• Vinyl-asbestos floor tiles
• Asbestos paper in filtration and insulation products
• Material in brake linings and clutch facings
• Textile products - Yarn, felt, tape, cord, rope
• Spray products used for acoustic, thermal, and fireproofing purposes

Occupations associated with asbestosis include the following:

• Insulation workers
• Boilermakers
• Pipefitters
• Plumbers
• Steamfitters
• Welders
• Janitors

The risk of uncontrolled removal of sprayed-on asbestos was highlighted in a study of two workers, in whom the presence and persistence of asbestos fibers and bodies in their bronchoalveolar lavage (BAL) fluid was noted even after several months. ^{[20, 21]}  A separate study provided a detailed assessment of the health hazards of exposure to asbestos-containing drywall accessory products. ^[22]

In 2014, the World Health Organization (WHO) estimated that 125 million people worldwide are exposed to asbestos in the workplace, that more than 100,000 people die each year from asbestos-related lung cancer, mesothelioma, and asbestosis, and that nearly 400 deaths are attributable to nonoccupational exposure to asbestos. ^[5]  

According to mortality data from the US National Center for Health Statistics (NCHS), 6290 deaths were attributed to asbestosis in the period 1999-2010, of which the majority (95%) were in White males (median age, 79 y). ^[23]  A 2024 study using data from the Global Burden of Disease (GBD) study reported that during the period 1990-2019, the overall number of deaths due to occupational exposure to asbestos increased by 20.2% in the United States, but the age-standardized mortality rate (ASMR) and the age-standardized disability-adjusted life years (DALYs) rate (ASDR) declined. ^[24]

A 2024 study reported that in 2019, occupational asbestos exposure was responsible for 239,330 deaths and 4,189,000 disability-adjusted life years (DALYs) globally. ^[25]  Over the period 1990-2019, deaths attributed to occupational asbestos exposure increased by 65.65% globally, and DALYs increased by 43.66%.

According to World Trade Center Health Registry estimates, about 410,000 people were exposed to asbestos when as much as 400 tons of it was released following the collapse of the the Twin Towers on September 11, 2001. ^[26]  Those at highest risk for developing 9/11-related illnesses were workers who participated in the rescue, recovery, and cleanup efforts at the sites of the towers, along with those living and working in lower Manhattan during the cleanup.

 A substantial amount of asbestos remains in buildings and eventually will be removed, either during remediation or renovations or demolition. It has been estimated that approximately 1.3 million workers in construction and general industry may be exposed to asbestos during maintenance activities or remediation of buildings containing asbestos. ^[23]  In the United States, vermiculite mined in Libby, Montana, was found to be contaminated with asbestos; this vermiculite was used in 70% of vermiculite insulation in the United States between 1919 and 1990. In a study of 128 Libby miners, 119 had asbestos-related findings on high-resolution computed tomography (HRCT). ^[27]  

Asbestos has not been mined in the United States since 2002, but in 2016, approximately 340 metric tons of asbestos was imported for use in the chloralkali industry to manufacture semipermeable diaphragms in electrolytic cells; in addition, an unknown quantity of asbestos was imported within manufactured products, possibly including brake linings and pads, building materials, gaskets, millboards, and yarn and thread, among others. ^[28]  In 2024, however, no asbestos was imported. ^[29]

Globally, bans on asbestos use are in place in several countries, including Australia, Japan, South Africa, and the nations of the European Union; asbestos use is restricted in the United States and Canada. However, persons who have been previously exposed to asbestos continue to be at risk for asbestosis and other asbestos-related diseases as a consequence of the long latency periods following exposure. ^{[30, 31]}  In addition, trends in developing countries and countries that are emerging as economic powers indicate an increasing problem with asbestos-related diseases. ^[32]

The following complications can result from asbestos exposure:

• Pulmonary hypertension
• Cor pulmonale
• Right-side heart failure
• Progressive respiratory insufficiency
• Malignancy

Progressive respiratory insufficiency

The risk factors for developing progressive respiratory insufficiency are as follows:

• Cumulative amount of asbestos inhaled
• Degree of dyspnea
• Cigarette smoking
• Combined pulmonary and pleural involvement
• Honeycombing visible on radiographs
• High number of neutrophils, eosinophils, and fibronectin in BAL fluid

Malignancy

A higher risk of lung carcinoma has been found in patients with asbestosis. Specifically, asbestos exposure raises the risk for bronchogenic carcinoma. Patients with asbestosis are also at risk for developing malignant mesothelioma and carcinomas of the upper respiratory tract, esophagus, biliary system, and kidney. Exposure to commercial materials made or contaminated with asbestos has been the main preventable cause of malignant mesothelioma. 

In a prospective cohort study (N = 544) examining the incidence of malignancy in patients with asbestosis from chrysotile exposure, Wang et al found the rate of occurrence to be 16.36% (n = 89). ^[33]  The standardized incidence ratios for the various malignancies were 16.61 for lung cancer, 175 for mesothelioma, 5.23 for breast cancer, and 8.77 for endometrial carcinoma.

A mortality study that included 3984 Italian shipyard workers employed in Genoa between 1960 and 1981 and followed them to 2014 reported a death rate of 83.6%, with excess mortality for all cancers, pleural mesothelioma, and cancers of the larynx and lung, as well as for respiratory diseases, including asbestosis. ^[34] Of the 399 deaths from lung cancer, 90 (22.6%) were attributed to asbestos exposure.

People who smoke are likely to develop chronic bronchitis and obstructive airway disease, and they are prone to respiratory tract infections. Moreover, people who smoke are at high risk for the development of bronchogenic carcinoma because asbestos and tobacco smoke have synergistic carcinogenicity. ^[35] Individuals who both smoke and are exposed to asbestos are several times more susceptible to the development of lung carcinoma than individuals without either exposure. ^[36]

Some studies have found that asbestos exposure alone, without a smoking history, increases the risk of lung carcinoma sixfold.

In addition, a meta-analysis of several studies of women who were occupationally exposed to asbestos found sufficient evidence for a causal association between asbestos exposure and ovarian cancer. ^[37] This association should be interpreted with caution, in that some cohort studies included in earlier meta-analyses reported disease misclassification for peritoneal mesothelioma. ^[38]

Concomitant diseases

Asbestosis may coexist with other asbestos-related diseases, including calcified and noncalcified pleural plaques, pleural thickening, ^[39] benign exudative pleural effusion, rounded atelectasis, and malignant mesothelioma of the pleura. A study of 102 asbestosis cases diagnosed since January 2001 found that pleural plaques were present in 94% (n = 96) and malignancies in 76% (n = 78; 38 lung cancers, 29 pleural mesotheliomas, 8 peritoneal mesotheliomas). ^[40]

Airway obstruction

A large study (N = 3660) that evaluated lung function in persons with previous occupational exposure to asbestos found no causal relation between airway obstruction and asbestos exposure. ^[41] No significant correlation was shown between pulmonary function parameters and cumulative asbestos exposure.

Patients should be informed regarding the work-related causes of asbestosis (see Medical Care). In addition, it is useful for patient education efforts to address the following questions.

What is asbestos?

Asbestos is a group of minerals shaped as long fibers. Sources of asbestos, up to the 1970s, included insulation, car brakes, ships, and construction materials. 

Who gets exposed to asbestos?

People get exposed to asbestos through their work. Occupations at high risk include construction workers, roofers, welders, and insulation workers, among others. Because asbestos can linger on articles of clothing, family members of people who work in these occupations may also be exposed if sufficient care is not taken.

What health problems can result from exposure to asbestos?

Asbestos can causes many health problems. The mnemonic CAP can serve as a useful reminder of the health problems associated with asbestos exposure, as follows:

• C (cancer) - Asbestos exposure has been associated with lung cancer and, rarely, mesothelioma
• A (asbestosis) - In asbestosis, asbestos causes damage to parts of the lung, which can make it difficult to breathe
• P (pleural disease) - When asbestos causes disease in the pleura (the thin outer covering of the lungs), it can cause fluid to accumulate in that space, and this fluid accumulation can lead to difficulty in breathing

Symptoms of asbestos exposure do not occur immediately after contact with the mineral. Some people may not have symptoms for 15-30 years. Most patients who develop asbestosis or another related disease due to asbestos exposure will have shortness of breath. Other symptoms include coughing up blood and chest pain. If any of these symptoms occur, medical attention should be sought.