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Preventing Hearing Loss Caused by Chemical 

(Ototoxicity) and Noise Exposure

Safety and Health Information Bulletin SHIB 03-08-2018

DHHS (NIOSH) Publication No. 2018-124

Introduction

Millions of workers are exposed to noise in the workplace every day and 

when uncontrolled, noise exposure may cause permanent hearing loss. 

Research demonstrates exposure to certain chemicals, called 

ototoxicants, may cause hearing loss or balance problems, regardless of 

noise exposure. Substances including certain pesticides, solvents, and 

pharmaceuticals that contain ototoxicants can negatively affect how the 

ear functions, causing hearing loss, and/or affect balance.

The risk of hearing loss is increased when workers are exposed to these 

chemicals while working around elevated noise levels. This combination 

often results in hearing loss that can be temporary or permanent, depending on the level of noise, the 

dose of the chemical, and the duration of the exposure. This hearing impairment affects many 

occupations and industries, from machinists to firefighters.

Effects on Hearing

Harmful exposure to ototoxicants may occur through inhalation, ingestion, or skin absorption. Health 

effects caused by ototoxic chemicals vary based on exposure frequency, intensity, duration, workplace 

exposure to other hazards, and individual factors such as age. Effects may be temporary or permanent, 

can affect hearing sensitivity and result in a standard threshold shift. Since chemicals can affect central 

portions of the auditory system (e.g., nerves or nuclei in the central nervous system, the pathways to the 

brain or in the brain itself), not only do sounds need to be louder to be detected, but also they lose clarity. 

Specifically, speech discrimination dysfunction, the ability to hear voices separately from background 

noise, may occur and involve:

 Compressed loudness: sound distortion.

 Frequency resolution: the inability to differentiate two sounds with similar frequency.

 Temporal resolution: the inability to detect time gaps between sounds.

 Spatial resolution: the inability to localize sound.

Speech discrimination dysfunction can also make working in noisy environments difficult and increase the 

risk of workplace injuries due to an inability to hear co-workers, environmental sounds and warning signals.

Source/Copyright: OSHA
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There is growing concern among occupational health and safety 

professionals that ototoxicant-induced hearing loss may go 

unrecognized since the measure for hearing loss does not indicate 

the cause. For example, audiometric tests are powerful tools that 

show hearing impairments (i.e., threshold shifts); however, they do 

not differentiate between noise and ototoxic causes.

Hearing loss can be even greater with exposure to both ototoxic 

chemicals and noise than exposure to either noise or the ototoxic 

chemical alone.1 Many ototoxic substances have a greater-thanadditive (e.g., synergistic) effect on hearing loss with noise 

exposure and in particular with impulse noise.2 Several studies have suggested that some ototoxic 

chemicals, such as certain solvents, might exacerbate noise-induced hearing loss even though the noise 

level is below OSHA's Permissible Exposure Limit (PEL).3

What are ototoxic chemicals and substances that contain ototoxicants? 

Ototoxic chemicals are classified as neurotoxicants, cochleotoxicants, or vestibulotoxicants based on the 

part of the ear they damage, and they can reach the inner ear through the blood stream and cause injury 

to inner parts of the ear and connected neural pathways.4 Neurotoxicants are ototoxic when they damage 

the nerve fibers that interfere with hearing and balance. Cochleotoxicants mainly affect the cochlear hair 

cells, which are the sensory receptors, and can impair the ability to hear. Vestibulotoxicants affect the hair 

cells on the spatial orientation and balance organs.5 The research on ototoxicants and their interactions 

with noise is limited. The dose-response, lowest observed effect level (LOEL) and no observed effect 

level (NOEL) have been identified in animal experiments for only a few substances.6

The following table includes examples of ototoxic chemicals grouped by substance class.7

Substance Class Chemicals

Pharmaceuticals 

*Ototoxicity at 

therapeutic doses is 

limited

Aminoglycosidic antibiotics (e.g. streptomycin, gentamycin) and some 

other antibiotics (e.g. tetracyclines), 

Loop diuretics* (e.g. furosemide, ethacrynic acid) 

Certain analgesics* and antipyretics* (salicylates, quinine, chloroquine)

Certain antineoplastic agents (e.g. cisplatin, carboplatin, bleomycin).

Solvents Carbon disulfide, n-hexane, toluene, p-xylene, ethylbenzene, 

n-propylbenzene, styrene and methylstyrene, trichloroethylene.

Asphyxiants Carbon monoxide, hydrogen cyanide and its salts, tobacco smoke

Nitriles 3-Butenenitrile, cis-2-pentenenitrile, acrylonitrile, cis-crotononitrile, 

3,3’-iminodipropionitrile.

Metals and Compounds Mercury compounds, germanium dioxide, organic tin compounds, lead.

Combined exposure: health 

effects below the noise PEL

OSHA standards require employers 

to maintain exposure to the specific 

substance at or below the PEL. 

However, synergistic effects from the 

combined ototoxicant and noise 

exposure could result in hearing loss 

when exposures are below the PEL.
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Table: Selected Ototoxicants

The table does not identify all known toxicants and, in addition, there is limited evidence that supports the 

ototoxicity of other chemicals including cadmium, arsenic, bromates, halogenated hydrocarbons, 

insecticides, alkylic compounds, and manganese.

The exposure threshold for ototoxicity varies for each chemical based on its compound family, properties, 

exposure route, exposure concentration and duration, synergy with noise, and noise exposure, along with 

an individual's risk factors.

Which industries are more likely to have ototoxicants? 

Industries that use potential ototoxicants include manufacturing, mining, utilities, construction, and 

agriculture. Manufacturing industry subsectors may include:

 Fabricated metal 

 Machinery

 Leather and Allied Product

 Textile and Apparel

 Petroleum

 Paper

 Chemical (including Paint)

 Furniture and Related Product

 Transportation Equipment (e.g. Ship and 

Boat Building)

 Electrical Equipment, Appliance and 

Component (e.g., Batteries)

 Solar Cell

Occupational activities that often have high noise exposure and could add synergistic effects when 

combined with ototoxicant exposure (i.e., occurring in the above industries) may include:

 Printing

 Painting

 Construction

 Manufacturing occupations in the 

subsectors listed above 

 Firefighting 

 Weapons firing

 Pesticide spraying

When specific ototoxicity information is not available, information on the chemical's general toxicity, 

nephrotoxicity, and neurotoxicity may provide clues about the potential ototoxicity. Most chemicals that 

are known to affect the auditory system are also neurotoxic and/or nephrotoxic. Information on whether a 

chemical produces reactive free radicals could also give some clues about the agent's potential 

ototoxicity.

Prevention

The first step in preventing exposure to ototoxicants is to know if they are in the workplace. One way to 

identify ototoxicants in the workplace is by reviewing Safety Data Sheets (SDS) for ototoxic substances 

and/or chemicals, and ototoxic health hazards associated with ingredients in the product. For example, 

Figure 1 shows an SDS where ototoxicants may be in a product.

Figure 1: Check the SDS.

Source/Copyright: OSHA
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Employers must provide health and safety information as well as training to workers exposed to 

hazardous materials, including ototoxic chemicals (see OSHA's hazard communication standard at 

29 CFR 1910.1200). The training must be in a language and vocabulary that the worker understands. 

Additionally, complaints from workers about hearing loss should include investigating SDSs for 

ototoxicants.

Controlling Exposure

Replacing a hazardous chemical with a less toxic chemical is an effective way to reduce exposure when 

ototoxicants are identified in the workplace.

If eliminating ototoxicants from the workplace is not possible, using engineering controls, such as isolation 

and enclosures to control exposure to ototoxicants and noise, may reduce risk for adverse health effects. 

Ventilation is also a recommended control method for ototoxicants.

Some administrative controls to consider include eliminating unnecessary tasks that cause noise or 

ototoxicant exposure, or operating noisy equipment when workers are not near.

Personal Protective Equipment (PPE)

Employers must assess and determine the appropriate PPE according to the general requirements in 

29 CFR 1910.132, the respiratory protection requirements in 29 CFR 1910.134, and the hand protection 

requirements in 29 CFR 1910.138.

Since many ototoxic substances can be absorbed through the skin, chemical-protective gloves, arm 

sleeves, aprons and other appropriate clothing can assist in reducing dermal exposure.

OSHA's occupational noise exposure standard at 29 CFR 1910.95 only requires audiometric testing at 

the noise action level (i.e., an 85-decibel 8-hour time-weighted average). However, wearing hearing 

protection and using audiometric testing to detect early signs of hearing loss, even in workers exposed 

below the action level and ototoxic chemicals below the PEL, may prevent hearing loss from their 

synergistic effects.

Information on Hearing Loss Prevention programs and their effectiveness is available online from 

the National Institute for Occupational Safety and Health (NIOSH) at www.cdc.gov/niosh/topics/noise/

preventhearingloss/hearlosspreventprograms.html.

Additional Information

OSHA can provide compliance assistance through a variety of programs, including technical assistance 

about effective safety and health programs, workplace consultations, and training and education. OSHA's 

On-Site Consultation Program offers free, confidential occupational safety and health services to small 

and medium-sized businesses in all states and several territories across the country, with priority given to 

high-hazard worksites. On-Site consultation services are separate from enforcement and do not result in 

penalties or citations. To locate the OSHA On-Site Consultation Program nearest you, visit 

www.osha.gov/consultation.

Workers' Rights

Workers have the right to:

 Working conditions that do not pose a risk of serious harm.

 Receive information and training (in a language and vocabulary the worker understands) about

workplace hazards, methods to prevent them, and the OSHA standards that apply to their workplace.
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 Review records of work-related injuries and illnesses.

 File a complaint asking OSHA to inspect their workplace if they believe there is a serious hazard or

that their employer is not following OSHA's rules. OSHA will keep all identities confidential.

 Exercise their rights under the law without retaliation, including reporting an injury or raising health

and safety concerns with their employer or OSHA. If a worker has been retaliated against for using

their rights, they must file a complaint with OSHA as soon as possible, but no later than 30 days.

For additional information, see OSHA's Workers page.

Contact OSHA

Under the Act, employers are responsible for providing safe and healthful workplaces for their employees. 

OSHA's role is to ensure these conditions for America's working men and women by setting and enforcing 

standards, and providing training, education and assistance. For more information, visit www.osha.gov or 

call OSHA at 1-800-321- OSHA (6742), TTY 1-877-889-5627.

Contact NIOSH 

To receive documents or more information about occupational safety and health topics, please contact 

NIOSH at 1-800-CDC-INFO (1-800-232-4636), TTY 1-888-232-6348, email: cdcinfo@cdc.gov or visit the 

NIOSH website at: www.cdc.gov/niosh.

1 European Agency for Safety and Health at Work. Combined Exposure to Noise and Ototoxic Substances. 2009. p 27.

2 Campo P., Venet T., Thomas A., Cour C., Brochard C., Cosnier F. Neuropharmacological and cochleotoxic effects of styrene. 

Consequences on noise exposures. Neurotoxicol Teratol. 2014 Jul-Aug; 44:113-20.

3 Occupational Safety and Health Administration. OSHA Technical Manual. Appendix D-3.

4 European Agency for Safety and Health at Work. Combined Exposure to Noise and Ototoxic Substances. 2009. p 9.

5 Johnson, A.C. and T.C. Morata. Occupational exposure to chemicals and hearing impairment, in Arbete och Hälsa, The Nordic 

Expert Group, Editor. 2010: Gothenburg. p. 1. Available at http://hdl.handle.net/2077/23240

6 European Agency for Safety and Health at Work. Combined Exposure to Noise and Ototoxic Substances. 2009. p 17.

7 Morata T.C., Dunn D.E., Sieber W.K. Occupational exposure to noise and ototoxic organic solvents. Archives of Environmental 

Health, 1994; 49(5):359-365.

This Safety and Health Information Bulletin is not a standard or regulation, and it creates no new legal 

obligations. The Bulletin is advisory in nature, informational in content, and is intended to assist 

employers in providing a safe and healthful workplace. Pursuant to the Occupational Safety and Health 

Act (OSH Act), employers must comply with hazard-specific safety and health standards and 

regulations promulgated by OSHA or by a state with an OSHA-approved state plan. In addition, 

pursuant to Section 5(a)(1), the General Duty Clause of the Act, employers must provide their 

employees with a workplace free from recognized hazards likely to cause death or serious physical 

harm. Employers can be cited for violating the General Duty Clause if there is a recognized hazard and 

they do not take reasonable steps to prevent or abate the hazard. However, failure to implement any 

recommendations in this Safety and Health Information Bulletin is not, in itself, a violation of the 

General Duty Clause. Citations can only be based on standards, regulations, and the General 

Duty Clause.