What is asbestos? The mineral, its properties and why it is dangerous

Asbestos is not a synthetic product. It is mined from rock, the same way iron ore or gold is mined, and it has been known to humans for over four millennia. Archaeologists have found asbestos fibers woven into 4,500-year-old Finnish pottery, Egyptian embalming cloths, and Roman oil-lamp wicks. The name itself comes from the ancient Greek ásbestos, meaning "inextinguishable" — a reference to its most striking property, the fact that it does not burn.

What turned asbestos from a curiosity into a global industrial commodity was the second industrial revolution. Between 1870 and 1970, annual world production climbed from almost nothing to more than five million tonnes. It was woven into fire-resistant textiles, mixed into cement and plaster, sprayed onto structural steel, molded into brake pads, insulation boards, pipe lagging, roofing tiles, gaskets and thousands of other products. At its peak in the 1970s, an estimated 3,000 industrial applications used some form of asbestos.

In regulation and medicine, the word "asbestos" refers to a specific group of six silicate minerals with a fibrous habit — meaning their crystals grow as long, thin fibers rather than compact blocks. These six minerals fall into two mineralogical families:

For most of the 20th century, no synthetic material could match asbestos on price and performance. Its combination of properties is genuinely unusual:

The same microscopic structure that makes asbestos industrially useful is what makes it lethal when inhaled. Unlike most dusts, asbestos fibers are long, thin, aerodynamic and biologically persistent. Once a fiber reaches the deep lung, the body cannot efficiently remove it. Macrophages — the immune cells that clean up inhaled particles — try to engulf the fiber, fail, and rupture. The released inflammatory chemicals damage surrounding cells. Over years and decades, that chronic inflammation and DNA damage lead to scarring (asbestosis) and cancer.

Three properties determine how dangerous a given asbestos exposure is: how much fiber reaches the lung (dose), how long the person is exposed (duration), and the physical dimensions of the fibers themselves. Long, thin fibers — especially those longer than 5 micrometers and thinner than 3 micrometers — are the most carcinogenic, because they penetrate deepest and resist clearance most strongly.

The International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organization, classifies all forms of asbestos — chrysotile, crocidolite, amosite, tremolite, anthophyllite and actinolite — as Group 1, "carcinogenic to humans". This is the highest classification, reserved for agents where the evidence of carcinogenicity is overwhelming. Asbestos has held this classification since 1977.

IARC links asbestos exposure to cancers of the lung, larynx and ovary, as well as to mesothelioma — a rare and almost always fatal cancer of the thin membrane lining the lungs, abdomen or heart. Mesothelioma is so strongly associated with asbestos that its presence in a patient is considered a sentinel event, meaning it is almost always caused by asbestos exposure even when the patient does not remember being exposed.

For decades, the asbestos industry argued that chrysotile — the curly, flexible form — was safer than amphibole asbestos because its fibers are cleared from the lung more quickly. This argument has been used to keep chrysotile legal in countries that banned amphibole forms, and it remains the core defense of ongoing mining operations in Russia, Kazakhstan, China and Brazil.

The scientific consensus is that this distinction does not justify continued use. WHO, IARC, ILO and the vast majority of independent public health agencies state clearly that all forms of asbestos cause mesothelioma and lung cancer, and that there is no level of exposure that can be demonstrated to be safe. In 2023, the EPA finalized a ban on the last remaining uses of chrysotile asbestos in the United States, explicitly rejecting the "safer form" argument.

Iceland became the first country to ban asbestos in 1983, followed by Norway, Sweden and Denmark later in the decade. The European Union banned all forms in 2005. Japan, Australia, South Africa and most of Latin America followed. Today more than 70 countries have a complete ban. Russia, China, India, Indonesia and Brazil together still account for the vast majority of continued global production and use.

Even in countries with a full ban, the problem is far from solved. Legacy asbestos remains in place in millions of buildings that were constructed between 1950 and the year of the national ban. In Spain alone, the National Institute for Occupational Safety and Health estimates that over 2 million tonnes of asbestos are still installed in schools, hospitals, public buildings and private housing.

Mesothelioma has an exceptionally long latency period — typically 20 to 50 years between first exposure and clinical disease. That means the people being diagnosed today were exposed in the 1970s and 1980s, when asbestos use was still widespread in most developed countries. Epidemiologists project that deaths from asbestos-related diseases in Europe will continue to rise until at least 2030, even though new use has been prohibited for almost twenty years.

The second, ongoing source of risk is in-place asbestos. Every renovation, demolition or accidental damage to a material containing asbestos has the potential to release fibers into the air. That is why the modern asbestos problem is less about new production and more about safe identification, management and removal of the enormous stock of material that was installed during the industrial century. That work is what certified asbestos professionals do.