Several chemicals have confirmed or probable links to multiple myeloma, a cancer of plasma cells in the bone marrow. The International Agency for Research on Cancer (IARC) classifies two chemicals as having sufficient evidence of causing multiple myeloma in humans: 1,3-butadiene and pentachlorophenol. A broader group of substances, including benzene, certain chlorinated solvents, formaldehyde, and pesticides, carry probable or limited evidence of increasing risk, particularly with prolonged occupational exposure.
Chemicals With the Strongest Evidence
The IARC, which is the cancer research arm of the World Health Organization, maintains a classification system for carcinogens based on the strength of available evidence. For multiple myeloma specifically, only two agents meet the highest standard of “sufficient evidence in humans.” The first is 1,3-butadiene, an industrial gas used in the production of synthetic rubber, plastics, and fuel. Workers in petroleum refining, rubber manufacturing, and chemical plants face the most significant exposure. The second is pentachlorophenol, a wood preservative widely used from the 1930s through the 1980s to protect utility poles, railroad ties, and lumber from fungi and insects. Though its use has been heavily restricted, it persists in the environment and in treated wood structures.
Chlorinated Solvents and Degreasing Agents
A family of chlorinated solvents used in manufacturing and cleaning shows consistent associations with multiple myeloma. A study of occupational exposures to six chlorinated solvents found that workers ever exposed to 1,1,1-trichloroethane (TCA) had 1.8 times the risk of developing multiple myeloma compared to unexposed workers. TCA is now classified by the IARC as having limited evidence for this cancer.
Trichloroethylene (TCE) and methylene chloride (DCM) also showed elevated risks, with odds roughly doubling for exposed workers. Longer duration and higher cumulative exposure to TCE corresponded to progressively higher risk. Perchloroethylene (PCE), the solvent most associated with dry cleaning, showed a similar pattern of increasing risk with increasing cumulative exposure.
The most common way workers encountered these chemicals was degreasing metal parts. Machine operators at automotive plants in Detroit and aircraft manufacturing facilities in Seattle were frequently exposed. Glues used on assembly lines and in packaging also contained DCM and PCE. For PCE specifically, dry cleaning work carried the highest intensity exposure.
Formaldehyde
Formaldehyde, used in building materials, adhesives, and furniture manufacturing, is linked to a twofold increase in multiple myeloma risk among workers with any occupational exposure. A large Italian case-control study found that daily exposure was associated with a sixfold increase in risk. Duration matters significantly: workers exposed for 36 years or more had 2.6 times the risk of unexposed individuals, with a clear upward trend as years of exposure increased.
Cabinet makers, parquetry workers, and furniture and plywood makers face the most relevant exposures. These workers encounter formaldehyde concentrations ranging from 0.5 to over 1.5 parts per million in workplace air. Even low-intensity exposure was associated with a statistically significant doubling of risk.
Pesticides and Agricultural Chemicals
Agricultural workers face some of the most elevated risks. People who regularly use herbicides and fungicides are roughly one and a half times more likely to develop multiple myeloma than the general population and eight times more likely to die from it. Insecticide exposure carries even higher individual risk, with a two- to fivefold increase in the odds of developing myeloma or its precursor condition, known as MGUS.
Among pesticide classes, insecticides show the strongest connection. Carbamates and organochlorines (such as DDT and cyclodienes) have the most consistent associations. One specific fungicide, captan, stands out: fewer than 17.5 lifetime days of exposure was associated with more than a threefold increase in myeloma risk. That’s a remarkably small amount of exposure for such a significant increase, and it underscores how potent some of these compounds may be for this particular cancer.
Agent Orange and Dioxins
Agent Orange, the herbicide mixture sprayed widely during the Vietnam War, contains dioxin compounds that are linked to multiple myeloma. The U.S. Department of Veterans Affairs recognizes this link as established. Veterans who develop multiple myeloma and were exposed to Agent Orange or other herbicides during military service do not have to prove a connection between their disease and service to qualify for VA health care and disability compensation. Surviving spouses and dependents of veterans who died from myeloma related to herbicide exposure are also eligible for survivors’ benefits.
Benzene, Gasoline, and Other Agents
Benzene is widely discussed as a myeloma risk factor, but the evidence is more nuanced than many people assume. The IARC classifies benzene as having “limited” rather than “sufficient” evidence for multiple myeloma specifically, placing it in Group 2A (probably carcinogenic for this cancer). A meta-analysis published in the Journal of Epidemiology concluded that benzene exposure alone is not likely to be a strong risk factor for myeloma, even though it clearly causes other blood cancers like leukemia.
Automotive gasoline, which contains benzene along with other hydrocarbons, also carries a Group 2A classification for multiple myeloma. Ethylene oxide, a sterilizing agent used in medical equipment processing and some manufacturing, and styrene, used in plastics and rubber production, round out the IARC’s list of probable agents. X-ray and gamma radiation also fall into this category.
Chemicals That Don’t Appear to Increase Risk
Not every chemical exposure popularly linked to cancer increases myeloma risk. PFAS, sometimes called “forever chemicals,” have not shown a positive association with multiple myeloma. A large study using the American Cancer Society’s cohort actually found negative associations between PFOS, PFOA, and PFNA levels and myeloma risk in both men and women, a pattern that held across multiple previous studies in highly exposed populations.
Permanent hair dyes, despite containing aromatic amines that raise concern for other cancers, also show no connection. A study of U.S. women found no increased myeloma risk among users of any hair coloring product, including dark permanent dyes used for 28 years or more.
How Chemical Exposure Leads to Myeloma
Chemical carcinogens damage DNA in plasma cells or their precursors, introducing mutations and chromosomal abnormalities that accumulate over time. Myeloma develops through a staged process. It typically begins as MGUS, a precancerous condition in which abnormal plasma cells are present but haven’t yet caused symptoms. Secondary genetic changes, including activation of cancer-promoting genes like MYC, KRAS, and NRAS, and loss of the tumor suppressor gene TP53, drive progression from this precursor state into active myeloma.
The time between chemical exposure and a myeloma diagnosis is substantial. The CDC uses a minimum latency period of four years for multiple myeloma following a known carcinogenic exposure, though typical latency is much longer. Most cases develop a decade or more after the relevant exposure began, which is one reason linking a specific chemical to an individual case can be difficult.
Who Faces the Highest Exposure Risk
Occupational exposure is the dominant route for most of the chemicals with strong myeloma links. The workers at greatest risk include rubber and plastics manufacturing employees (butadiene, styrene), agricultural workers and pesticide applicators (insecticides, herbicides, fungicides), furniture makers and woodworkers (formaldehyde), metal workers and machinists (chlorinated solvents from degreasing), dry cleaners (perchloroethylene), and petroleum refinery workers (benzene, butadiene). Military veterans exposed to Agent Orange or similar tactical herbicides carry a recognized, compensable risk. For the general population, ambient chemical levels are far lower than occupational settings, and background exposure to these chemicals is not considered a major driver of myeloma cases.