What causes a Hearing Loss?

Causes and types of Hearing Loss

The majority (90%) of children with hearing loss are born to parents with normal hearing¹¹. 50% of hearing loss is due to genetics while the other 50% is due to non-genetic and unknown causes².

Genetic/ hereditary hearing loss (HL) may present at birth/ at a later age (e.g. in adulthood) and may/ may not occur as part of a syndrome (e.g. Down syndrome). A non-syndromic HL means there is no other deficit except with hearing. Non-genetic HL is most often a result of illness (e.g. mumps, scarlet fever, jaundice), bacterial and viral infections or trauma that damages the hearing system⁴.

This can occur before, during or after birth¹¹. Some examples of infections include Rubella (German measles), Herpes, Syphillis, Toxoplasmosis (Cat-scratch disease), Cytomegalovirus (CMV) and Meningitis. Birth complications, such as, prematurity, low birth weight, breathing problems, heart abnormality and prolonged mechanical ventilation are also risk factors.

Unfortunately, some medications used to treat these complications or infections can produce a permanent hearing loss^11,12. Genetic testing and careful questioning (case history) may help identify the cause of the HL, but sometimes, this remains unclear or unknown⁵.

Types of Hearing Loss

Hearing loss is described and managed according to which part of the ear is affected. As you can see below, the ear is divided into outer, middle and inner ear segments.

1. Conductive Hearing Loss (CHL)

HL caused only by outer and/or middle ear problems is called a CHL. This can be temporary (e.g. excessive earwax, middle ear infection) or permanent (absent ear canal/ middle ear bones).

Middle ear infections are a common cause of temporary CHL among young children. This is because the Eustachian Tube (see Figure 2 above), which connects the middle ear to the throat, is easily blocked during a cold or flu.

In comparison to adults, children are at greater risk because their tube is shorter and more horizontal. When this tube is closed, middle ear pressure is not equal to the outer air pressure, giving the sensation of ‘blocked ears’ (like when you are in the plane).

This can cause a build up of fluid, which may/ may not be infected by the cold, to produce a temporary HL. Sometimes, infections can persist to produce more severe consequences³.

Therefore, a GP consultation is advised if your child demonstrates any sign of ear infections or hearing difficulties. As management of CHL is usually medical and/or surgical, hearing aids are often unnecessary if hearing returns to normal after treatment¹¹.

2. Sensorineural Hearing Loss (SHL)

SHL is due to a problem in the inner ear, that is, damage to the cochlea (hearing organ) or the hearing nerve. This may be due to genetics, medication, bacterial/ viral infections, birth complications or a malformed inner ear. SHL is the most common type of permanent HL and cannot be medically treated¹¹.

Besides reducing loudness, it also reduces sound clarity. A hearing aid can help by making sounds louder. However, as it cannot replace the intricate workings of the cochlea, hearing will still not be perfect¹.

When only the hearing nerve is affected, the HL is called Auditory Neuropathy/ Dysynchrony. It is not as common as SHL and unlike SHL; the problem lies in the delivery and processing of sound by the brain. There are many causes for this condition, including, genetics, head trauma, severe jaundice, lack of oxygen, infectious disease and neurological disorders⁵.

3. Mixed Hearing Loss (MHL)

A MHL is when both a CHL and SHL exist. Although medical treatment of the CHL will improve hearing, a hearing loss will still present due to the permanent sensorineural component¹¹.

4. Unilateral Hearing Loss (UHL)

UHL means that the hearing loss is in only one ear. UHL can be present at birth (genetic/ pregnancy complications), acquired from illness (mumps/ meningitis) or due to unknown causes. Medical investigation is required as UHL is sometimes a sign of other more serious health conditions.

Depending on the situation, a hearing aid may/ may not be required. However, monitoring and protection of the normal ear is very important.

Communication/ listening strategies, to be used at home and school, will also help with difficulties locating sounds and hearing in noisy situations^{1, 11.}