Types of Hearing Loss and Their Causes

Not all hearing loss is the same. There are different types of hearing loss and different reasons that hearing can be impaired. Here is an overview.

Sudden hearing loss

Sudden hearing loss is defined as the loss of 30 decibels over 3 frequencies for at least 72 hours. Sudden hearing loss occurs in a matter of a few hours or days. Some people wake up and discover overnight hearing loss. Sudden hearing loss is serious and requires immediate attention. If you ever experience sudden hearing loss, call the doctor right away.

Causes of sudden hearing loss

While there are many reasons for sudden hearing loss, in more than 80 percent of cases the cause is never identified. Sudden hearing loss can be caused by:

• Infectious diseases
• Inner ear issues
• Head injury
• Ototoxic drugs
• Circulatory problems
• Neurologic diseases
• Autoimmune disorders

Noise-induced hearing loss

Noise-induced hearing loss is either temporary or permanent. Some noise-induced hearing loss happens so gradually that it isn’t even noticed until a substantial hearing loss has occurred. Other noise-induced hearing loss happens immediately as a result of trauma or exposure to an explosion or other loud noise. It is the result of damage to the hair cells in the cochlea.

Causes of noise-induced hearing loss

Exposure to loud noises can be a continuous event (like the noise from machinery at work) or a one-time event (such as an explosion). Both types of exposure to noise damages the hair cells and causes noise-induced hearing loss. Noises that can cause hearing loss are:

• Explosions
• Firearms noise
• Snowmobile, motorcycle or ATV noise
• Machinery (wood or metal working lathes, presses, etc. or lawn equipment)
• Loud music in a club or concert hall (105 decibels or more)

The noise-induced hearing loss after a one-time event like an explosion or a head trauma may appear to be temporary because hearing returns within 16 to 48 hours. However, permanent damage may have occurred.

Genetic mutation

Some people are born without hearing because of a genetic mutation. Genes are the blueprints that tell bodies how to grow and when to specialize. If one of the genetic instructions is not correct, it is a mutation. Certain mutations run in families but others occur independently. Most genetic mutations that cause hearing loss occur without any other symptoms or mutations. About 30 percent occur with another mutation, such as one for blindness. Genetic researchers have identified a mutation in the GJB2 gene that causes defects in the cochlea.

Causes of genetic mutation

Researchers are still working to crack the genetic code and understand why mutations occur. Some are hereditary and some occur in the absence of the mutation in either parent. Acquired (or somatic) mutations can occur as a result of environmental exposure or can be a simple mistake made when DNA is copied during cell division.