Hearing Loss: Types, Causes and Contributing Factors

Hearing loss can manifest with varying types and levels of severity, and has many causes. Hearing loss can have a significant impact on an individual's life and may even increase the chance of developing speech disorders or communication disorders if the hearing loss is not addressed. Early identification of hearing loss is important for effective intervention, which can involve obtaining a hearing aid, using a manual communication system, or reducing noise exposure to avoid further damage.

Hearing Loss Types

Hearing loss tests examine both hearing acuity at various frequencies and the ability to understand speech. Two types of hearing are tested:

• Air conduction hearing is the ability to hear sounds transmitted to the hearing mechanism through the air.
• Bone conduction hearing represents the ability to interpret sound information that is conducted through bones (including the forehead).

Results of hearing tests are presented on a chart called an "audiogram," which shows hearing thresholds at each frequency for each ear. The chart shows both air conduction and bone conduction hearing thresholds.

Hearing loss presents as one of three different types:

• Conductive hearing loss is a problem with the air conduction method of hearing, indicating a problem in the outer or middle ear. Conductive hearing loss can be recognized in test results because bone conduction hearing thresholds are lower than air conduction hearing thresholds (or even normal).
• Sensorineural hearing loss affects the hearing mechanism at the sensory (cochlea) or neural (auditory nerve) level. Hearing test results show both bone conduction and air conduction to be impaired.
• Mixed hearing losses show both conductive and sensorineural hearing loss, often with different types of hearing loss at different frequencies.

Causes of Hearing Loss

Different types of hearing loss can have a variety of sources.

• Aging: Hearing loss due to aging, which has no other discernable cause, is called presbycusis.
• Genetics: Congenital hearing loss is present at birth, and includes genetic disorders of hearing and inherited hearing loss.
• Illness: Disease such as toxoplasmosis, cytomegalovirus, and rubella pose high risk when mother has infection during pregnancy, or when the infection is transmitted during birth. Meningitis and otitis media also carry risk for hearing damage.
• Injury: A puncture to the tympanic membrane (eardrum) or blow to the head can damage the structure of the hearing mechanism and lead to hearing loss.
• Noise exposure: Exposure to loud noise (over 85 dB) can lead to hearing loss.
• Ototoxic drugs: Some drugs and medications (including some chemotherapeutic drugs, and some antibiotics, especially aminoglycosides) can cause damage to the cochlea. Hearing loss can be temporary or permanent.

Several other conditions may cause hearing loss disorders, including diseases (such as Meniere's disease and otosclerosis) and tumors. A hearing test, along with a detailed medical history, can help to identify the type and cause of hearing loss, associated disorders, and can indicate an appropriate method for addressing the hearing loss.

Resources

American Speech-Language-Hearing Association (n.d.). Causes of hearing loss in adults. Retrieved February 5, 2010, from American Speech-Language-Hearing Association Web site: http://www.asha.org/public/hearing/disorders/causes_adults.htm.

American Speech-Language-Hearing Association (n.d.). Causes of hearing loss in children. Retrieved February 5, 2010, from American Speech-Language-Hearing Association Web site: http://www.asha.org/public/hearing/disorders/causes.htm.

American Speech-Language-Hearing Association (n.d.). Type, degree, and configuration of hearing loss. Retrieved February 15, 2010, from American Speech-Language-Hearing Association Web site: http://www.asha.org/public/hearing/disorders/types.htm.

Merck (2007). Drug-induced ototoxicity. Retrieved February 5, 2010, from Merck Web site: http://www.merck.com/mmpe/sec08/ch086/ch086d.html#BABBAHDJ.

My Baby's Hearing (n.d.). Causes of hearing loss: non-genetic hearing loss. Retrieved February 5, 2010, from My Baby's Hearing Web site: http://www.babyhearing.org/hearingamplification/causes/nongenetic.asp.