What are ototoxic chemicals?

Ototoxic chemicals are substances like medication and chemicals that are harmful to your hearing and balance. Ototoxic chemicals can cause hearing loss and below is a list of common ototoxic chemicals:

• Arsenic – Found in parasites and microorganism inhibitors
• Benzene – Found in plastic, paints, cigarette smoke
• Carbon disulfide – Found in pesticides
• Carbon monoxide – Cigarette smoke, vehicles, cooking stoves, etc.
• Styrene – Found in plastics and insulating materials.
• Trichloroethylene – Found in paints, waxes, pesticides, lubricants, etc.
• Toluene – Found in lacquers, adhesives, rubber, etc.
• Xylene – Paints, thinners, etc.

Some of those substances stated above may be in products used at home, such as paints, detergents, and other cleaning agents. 

Medications causing hearing loss as a side effect include:

Drug category	Class of drug	Subclass of drug	Examples
Anti-infective	Antibiotics	Aminoglycosides Macrolides Quinolones Others	Neomycin, gentamicin, amikacin Erythromycin, clarithromycin Ofloxacin, ciprofloxacin Tetracyclines, vancomycin
	Antivirals		Ganciclovir, Zalcitabine, ribavirin+ interferon
	Antifungals		Amphotericin, flucytosine
	Antimalarials		Chloroquine, mefloquine, quinine
Analgesics	Non-steroidal Anti-inflammatory		Aspirin, Indomethacin, ibuprofen Ketorolac, sulindac
Anticancer drugs	Cytotoxics	Platinum compounds Vinca alkaloids Others	Cisplatin, Carboplatin, Oxaliplatin Vindesine, Vinblastine, vincristine Bexarotene, taxane
Cardiac and vascular drugs	Diuretics	Loop diuretics Carbonic anhydrase	Frusemide, Bumentanide, Torasemide Acetazolamide

What are the effects of ototoxic chemicals?

Ototoxic chemicals can cause damage to the auditory nerve (hearing nerve) and they can enter the body in various ways. These chemicals can enter the body through oral methods (eating or drinking), penetrate the skin barrier (go through the skin), or through inhalation (breathed). The chemicals then enter the bloodstream and once they enter the bloodstream, they can enter the hair cells in the cochlear, auditory nerve, and other central parts of the auditory system and damage hearing. The effects caused by ototoxic chemicals can continue even when a person is no longer exposed to the ototoxic chemical. This is dependent on how much of the chemical has accumulated in the body.

Effects of ototoxicity caused by medication

Common side effects of ototoxicity caused by medication include hearing loss and tinnitus (ringing, buzzing, hissing sound in the ear). Hearing loss causes difficulty in speech discrimination, fullness, and dizziness. A higher dosage of ototoxic medication can result in hearing loss worsening.

How do ototoxic chemicals cause hearing loss?

Ototoxic chemicals can damage the hair cells in the cochlea (the hearing organ). Sound vibrations travel from the outer ear to the inner ear. The fluid in the cochlea (organ of hearing) moves due to the vibrations that cause the cochlea’s hair cells to move. The vibrations change into electrical energy and move to the brain, where they are recognized as sound. When there is a problem with sound traveling from the ear to the brain, this results in hearing loss. When the hair cells on the cochlea are damaged, they cannot move efficiently, causing hearing loss. Hearing loss caused by ototoxic chemicals can cause any degree of hearing loss. This is dependent on the type of chemical, exposure duration, frequency, and age. Hearing loss caused by ototoxic chemicals can worsen if a person is also exposed to loud noise. Exposure to both ototoxic chemicals and noise can cause temporary or permanent hearing loss. This depends on the noise level, level of exposure to noise, age, type of ototoxic chemical, exposure duration to the ototoxic chemical, and how often a person is exposed to it.

Consequences of hearing loss

Ototoxic-induced hearing loss has dire consequences as hearing loss affects communication, literacy, academic, vocational, and socio-emotional development. Even mild hearing loss can affect academic development. Ototoxic hearing loss also potentially contributes to long-term vulnerability to noise-induced hearing loss.

What are the signs of hearing loss caused by chemicals?

Ototoxic chemicals can cause hearing loss and balance problems. Signs of hearing loss are:

• Tinnitus (ringing, buzzing, or hissing sound in the ear/s);
• Difficulty hearing in background noise;
• Difficulty discriminating between words that sound similar;
• A feeling of fullness in the ear/s

Signs of a balance problem are:

• Headache
• A feeling of fullness in the ear/s
• Unclear vision
• Dizziness

If you start experiencing any of the signs stated above, you should speak to your hearing healthcare professional. Your hearing healthcare professional would conduct various tests to determine if you have a hearing problem or not. If you are diagnosed with permanent hearing loss, then a hearing aid is one of your options to help you hear and communicate better. 

A hearing aid will help make the sounds louder for you to hear and offer better clarity. Louder sounds do not mean clear sounds. Since ototoxic chemicals would most likely damage the central part of the auditory system, hearing speech clearly would be a problem. Using a hearing aid that offers both loudness and speech clarity would be the best recommendation. Choosing a hearing aid that allows more room for increasing the loudness, and clarity would be better if you are still going to be exposed to ototoxic chemicals and/or hazardous noise levels, as it could worsen your hearing.

How can you protect yourself against ototoxic chemicals and improve your hearing?

• Try using less ototoxic chemicals.
• If it cannot be replaced, the environment should be well ventilated. The OSHA has outlined guidelines at the workplace. Speak to your safety officer regarding these guidelines.
• Use personal protective equipment. This can help reduce the chemicals from entering your body. E.g., respirators, gloves, etc.
• Hearing conservation program – At the workplace, a hearing conservation program should be implemented if their workers come in contact with ototoxic chemicals.
• Read the labels of household detergents and other cleaning products and follow the safety instructions.
• If you are unsure if a certain chemical is ototoxic, it would be best to avoid using it until you are certain it is not.

Certain ototoxic medications cannot be avoided as it helps with life-threatening conditions. In situations where ototoxic medication cannot be replaced with medication that is not ototoxic or less ototoxic then it is best to have your hearing status monitored regularly. Speak to your doctor and hearing healthcare professional on ototoxic medication and ototoxic chemicals, and how you can protect your hearing from damage.