When most people think about occupational hearing loss, they immediately think about noise – grinders, machinery, power tools, aircraft, firearms, or other loud equipment. But noise is not the only workplace hazard capable of damaging hearing. Some chemicals can damage the auditory system, and they may make noise even more dangerous.
In the News: Millions of Workers Exposed
In April 2026, the National Institute for Occupational Safety and Health (NIOSH) highlighted new occupational hearing-loss surveillance information drawing atten tion to a hazard that remains poorly recognized – ototoxic chemicals. NIOSH estimates that approximately 22 million U.S. workers, or about 13% of the workforce, were exposed to ototoxic chemicals during the previous year. Even more concerning, approximately seven percent of workers were exposed to both hazardous occupational noise and ototoxic chemicals.
Manufacturing workers face substantial risks. NIOSH estimates that approximately 24% of these workers were exposed to ototoxic chemicals, while about 17% were exposed to both hazardous noise and ototoxic chemicals. (Notably, the mining and construction sectors reported even higher exposure rates, at 49% and 30%, respectively.) These findings are important because traditional hearing conservation efforts have historically focused primarily on measuring decibels. Increasing evidence shows that an effective hearing-loss prevention program should also consider what chemicals workers are breathing, absorbing through their skin, or otherwise encountering during the workday.
What is an Ototoxicant
An ototoxicant is a chemical or substance that can damage structures or pathways involved in hearing and balance. Depending on the substance, the effects may involve the inner ear, auditory nerve, or portions of the nervous system responsible for processing sound. Occupational exposure may occur through inhalation, skin absorption, or ingestion.
Ototoxic exposures can contribute to temporary or permanent hearing loss, tinnitus (ringing or buzzing in the ears), difficulty understanding speech (particularly in background noise), problems distinguishing sounds, balance disturbances, and increased susceptibility to noise-induced hearing loss. One of the most important occupational health concerns is the interaction between chemicals and noise. Exposure to certain ototoxicants and noise together can produce greater hearing damage than exposure to either hazard alone. In some circumstances, certain chemicals may increase the risk of hearing damage even when workplace noise is below the level normally considered hazardous by itself.
Which Chemicals Should Be of Concern
Ototoxicants occur in numerous industries and occupations. Important groups of ototoxicants include several categories of chemicals that may be encountered in occupational settings. Organic solvents – such as toluene, styrene, xylene, and ethylbenzene – are commonly used in paints, coatings, adhesives, degreasers, plastics manufacturing, and other industrial processes and have been associated with adverse effects on hearing. Asphyxiants – including carbon monoxide and hydrogen cyanide – may also affect the auditory system, particularly when exposure interferes with the body’s ability to deliver or use oxygen. Metals – such as lead and certain mercury compounds – can affect the nervous system and may contribute to auditory dysfunction following sufficient exposure. Nitriles, including acrylonitrile, which may be encountered in chemical and plastics manufacturing have potential ototoxic properties. Certain pesticides – including some organophosphates and pyrethroids – have also been associated with adverse effects on hearing and the nervous system. Finally, some pharmaceuticals have well-established ototoxic effects and can damage hearing or balance.
Because workers may encounter these substances while also being exposed to hazardous noise, industrial hygienists should evaluate both chemical and noise exposures when assessing the potential risk of occupational hearing loss. Workers potentially affected include employees in manufacturing, construction, painting, printing, automotive work, chemical production, firefighting, agriculture, waste management, metalworking, petroleum operations, and other occupations involving solvents, fuels, combustion products, pesticides, or metals. A worker using a solvent-based product near operating machinery, for example, may be facing two hearing hazards simultaneously: chemical exposure and noise exposure.
Why Hearing Protection Alone May Not Be Enough
Earplugs and earmuffs are important components of hearing conservation, but they cannot prevent a chemical from entering the body.
Imagine a worker exposed to toluene while working around noisy machinery. Hearing protection may reduce the noise reaching the worker’s ear, but it does nothing to prevent inhalation or skin absorption of toluene. This means occupational hearing-loss prevention should not automatically stop when the noise dosimeter shows an exposure below an occupational exposure limit.
Industrial hygienists should ask another question: Are workers simultaneously exposed to substances capable of affecting hearing? If the answer is yes, the exposure assessment should consider the combined risk. In some cases, occupational exposure limits for certain ototoxic chemicals may need to be set lower when noise is also present, as the combined effect can damage hearing at levels that would be considered safe for each hazard individually.
Identifying Ototoxicants in the Workplace
A good starting point is the workplace chemical inventory. Safety Data Sheets (SDSs) should be reviewed – particularly Section 2 (Hazard Identification), Section 8 (Exposure Controls/Personal Protection), and Section 11 (Toxicological Information). However, the absence of the word “ototoxic” on an SDS does not mean that the chemical poses no auditory hazard; because this is not a required GHS hazard category, and manufacturers may not always test for or list this specific effect. NIOSH specifically recommends identifying chemicals with known or suspected ototoxic properties before exposure occurs. Industrial hygienists and safety professionals should pay particular attention when workers experience both chemical exposure and significant workplace noise.
Controlling the Hazard
Ototoxicants should be addressed using the same hierarchy of controls applied to other occupational hazards.
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Elimination and substitution: Determine whether the ototoxic chemical is necessary. Whenever practical, replace it with a less hazardous material or process.
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Engineering controls: Use enclosure, isolation, local exhaust ventilation, process ventilation, automation, and other controls to reduce chemical exposure. Noise sources should likewise be controlled at their source whenever feasible.
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Administrative and work-practice controls: Limit exposure duration; restrict access to high-exposure areas; keep containers closed when not in use; provide appropriate training; and prevent unnecessary simultaneous chemical and noise exposures.
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Personal protective equipment (PPE): Select appropriate gloves, protective clothing, respiratory protection, hearing protection, and other PPE based on the exposure assessment – realizing that hearing protection addresses the noise pathway, not chemical absorption.
Audiometric Surveillance
When ototoxic exposures are identified, particularly when combined with occupational noise, employers should consider whether affected workers need enhanced hearing surveillance. A standard audiogram can identify changes in hearing sensitivity, although determining whether a hearing loss resulted from noise, chemicals, aging, or a combination of factors can be difficult. This makes prevention and early recognition particularly important.
Conclusion
Hearing conservation isn’t only about what workers hear. It is also about what they breathe, touch, and absorb. For decades, occupational hearing conservation was largely treated as a noise problem.
We now know that the picture is more complicated. A worker may have a noise exposure below a traditional occupational limit and still face increased hearing risk because of simultaneous exposure to an ototoxic chemical. Conversely, reducing chemical exposure may be an important component of preventing occupational hearing loss.
Five Questions to Ask During the Next Workplace Assessment
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Are employees exposed to solvents, metals, asphyxiants, pesticides, or other potential ototoxicants?
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Are those employees also exposed to workplace noise?
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Have the SDSs and available toxicological information been reviewed for potential auditory effects?
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Can chemical or noise exposure be eliminated or reduced through engineering controls or substitution?
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Should potentially exposed workers be included in audiometric or medical surveillance?
How HETI Can Help
HETI’s staff of industrial hygienists, environmental scientists, and technical professionals can assist employers in identifying and evaluating workplace exposures to ototoxic chemicals and hazardous noise. Our services include reviewing chemical inventories and Safety Data Sheets (SDSs) for potential ototoxicants; conducting workplace exposure assessments and noise monitoring; evaluating situations where workers may experience combined chemical and noise exposures; and recommending appropriate engineering, administrative, and personal protective controls. HETI can also assist with hearing conservation program evaluations, employee training, exposure-control strategies, and regulatory compliance support to help organizations reduce the risk of occupational hearing loss.
References: Masterson, E. A., & Mobley, A. (2026). Chemicals and Hearing Loss: A Connection. National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention. April 2, 2026. https://www.cdc.gov/niosh/bulletin/2026/ ototoxicants.html
National Institute for Occupational Safety and Health. (2024, February 16). Occupational hearing loss surveillance. Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/noise/surveillance/index.html
For further information on HETI’s risk management and environmental health & safety services, please contact us.
Daniel Farcas, PhD, CIH, CSP, CH