Causes of Hearing Loss

 

Congenital Hearing Loss (Hearing Loss at Birth)

Non-genetic factors can account for about 25% of congenital hearing loss. Non-genetic factors that are known to cause congenital hearing loss include:

 

• Maternal infections, such as rubella (German measles), cytomegalovirus, or herpes simplex virus

• Prematurity

• Low birth weight

• Birth injuries

• Toxins including drugs and alcohol consumed by the mother during pregnancy

• Complications associated with the Rh factor in the blood/jaundice

• Maternal diabetes

• Toxemia during pregnancy

• Lack of oxygen (anoxia)

 

Genetic factors (hereditary) are thought to cause more than 50% of all hearing loss. Hearing loss from genetic defects can be present at birth or develop later on in life. Most genetic hearing loss can be described as autosomal recessive or autosomal dominant. Other, more rare types of genetic hearing loss include X-linked (related to the sex chromosome) or mitochondrial inheritance patterns.

 

Acquired Hearing Loss (Hearing Loss After Birth)

Acquired hearing loss is a hearing loss that appears after birth. The hearing loss can occur at any time in one’s life, as a result of an illness or injury. The following are examples of conditions that can cause acquired hearing loss:

 

• Ear infections (very common in children)

• Medications that are toxic to the ear

• Meningitis

• Measles

• Encephalitis

• Chicken pox

• Flu

• Mumps

• Head injury

• Noise exposure

Noise: How loud is too loud?

Loud noise can be very damaging to hearing. Both the level of noise and the length of time you listen to the noise can put you at risk for noise-induced hearing loss. Noise levels are measured in decibels, or dB for short. The higher the decibel level, the louder the noise. Sounds that are louder than 85 dB can cause permanent hearing loss. The hearing system can be injured not only by a loud blast or explosion but also by prolonged exposure to high noise levels.

 

How loud is too loud?

The noise chart below lists average decibel levels for everyday sounds around you.

 

Painful

150 dB = fireworks at 3 feet

140 dB = firearms, jet engine

130 dB = jackhammer

120 dB = jet plane takeoff, siren

 

Extremely Loud

110 dB = maximum output of some MP3 players, model airplane, chain saw

106 dB = gas lawn mower, snowblower

100 dB = hand drill, pneumatic drill

90 dB = subway, passing motorcycle

 

Very Loud

80–90 dB = blow-dryer, kitchen blender, food processor

70 dB = busy traffic, vacuum cleaner, alarm clock

 

Moderate

60 dB = typical conversation, dishwasher, clothes dryer

50 dB = moderate rainfall

40 dB = quiet room

 

Faint

30 dB = whisper, quiet library

 

How can I tell if I am listening to dangerous noise levels?

 

• You must raise your voice to be heard.

• You can’t hear someone 3 feet away from you.

• Speech around you sounds muffled or dull after you leave the noisy area.

• You have pain or ringing in your ears (this is called “tinnitus”) after exposure to noise.

 

How can loud noise damage hearing?

 

Understanding how we hear will help you to understand how loud noise can hurt your hearing.

One of the most common bad effects of loud noise on hearing is a permanent hearing loss. This happens in the following way:

 

• The loud sound is collected by the ear as sound waves. The sound waves travel down the ear canal toward the eardrum with enough force to disrupt the delicate hearing system. If the sound is loud enough, it can dislodge the tiny bones of the middle ear.

• The loud sound passes through the middle ear and travels to the inner ear, also known as the cochlea. The tiny hair cells lining this fluid-filled chamber can be damaged as the loud sound reaches the inner ear.

• Only healthy hair cells can send electrical impulses to the brain. It is in the brain that the sound is understood and interpreted. Hair cells damaged by loud sound cannot send the impulse to the brain for interpretation.

• Intense brief noises, like a firecracker or an explosion, can damage hair cells, as can continuous and/or repeated exposure to high levels of noise.

• Once the hair cells are damaged, there is no current treatment to repair them.

 

Types of Hearing Loss

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Hearing loss can be categorized by which part of the auditory system is damaged. There are three basic types of hearing loss:

 

Conductive Hearing Loss

Conductive hearing loss occurs when sound is not conducted efficiently through the outer earcanal to the eardrum and the tiny bones (ossicles) of the middle ear. Conductive hearing loss usually involves a reduction in sound level or the ability to hear faint sounds. This type of hearing loss can often be corrected medically or surgically.

Some possible causes of conductive hearing loss:

 

• Fluid in the middle ear from colds

• Ear infection (otitis media)

• Allergies (serous otitis media)

• Poor eustachian tube function

• Perforated eardrum

• Benign tumors

• Impacted earwax (cerumen)

• Infection in the ear canal (external otitis)

• Swimmer’s Ear (otitis ecxterna)

• Presence of a foreign body

• Absence or malformation of the outer ear, ear canal, or middle ear

 

Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL) occurs when there is damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain. Most of the time, SNHL cannot be medically or surgically corrected. This is the most common type of permanent hearing loss.

SNHL reduces the ability to hear faint sounds. Even when speech is loud enough to hear, it may still be unclear or sound muffled.

 

Some possible causes of SNHL:

 

• Illnesses

• Drugs that are toxic to hearing

• Hearing loss that runs in the family (genetic or hereditary)

• Aging

• Head trauma

• Malformation of the inner ear

• Exposure to loud noise

 

Mixed Hearing Loss

Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss (SNHL). In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

 

If you think you may have hearing loss visit the Hearing Loss Checklist page and consider scheduling an appointment for a FREE hearing test.

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