Sensorineural hearing loss stems from damage to or abnormalities of the small hair cells of the organ of the Corti which is in the cochlea, or nerves that sense the sound waves entering the ear (Vestibulocochlear nerve) or the auditory portions of the brain, although this is not common. Most sensorineural hearing loss is due to the poor functioning of hair cells.

These hair cells may be abnormal at birth or damaged later either by external causes or intrinsic abnormalities.

Typical causes

Sensorineural hearing loss can occur for a number of reasons including:

• Activities
  • Acoustic ear trauma is the prolonged exposure to loud noise. Could be a rock concert, car sound system, children's toys, crowds, machinery or power tools in the work environment, even living close to an airport. A single event such as an explosion can result in permanent or temporary loss.
  • Common factors from noise trauma include:
    • Generally the hair cells on the cochlea become less sensitive.
    • Hearing loss is usually centered around the frequencies 3000, 4000 or 6000 Hz.
    • As damage progresses, other frequencies become affected
    • The louder the noise, the more accelerated the damage. For example, according to the National Institute of Occupational Health and Safety (1998): Safe exposure to noise at 85dB is 8 hours, while safe exposure at 91dB is only 2 hours. YThis can vary by individual.
  • Barotrauma or pressure trauma results from sudden or rapid changes in air or water pressure and affects enclosed air cavities in the body such as the middle ear. Barotrauma is also called ear squeeze in diving circles

• Injury and other
  • Head trauma resulting in the fracture of the temporal bone can affect the nerves of the auditory system and thus hearing. This can result in permanent or temporary hearing loss.
  • Just plain getting older
  • Fetal alcohol syndrome, or babies born to alcoholic mothers can result in Sensorineural hearing loss over 50% of the time due to malnutrition from alcohol intake during the pregnancy

• Medical conditions and drugs
  
  • The following illnesses or condition can damage the auditory nerve:
    • Measles
    • Meningitus
    • Acoustic neuroma, a tumour which grows on the auditory nerve and can result in a ringing in the ears
    • AIDS and HIV, in certain cases
    • Influenza
  • The following illnesses or conditions may affect the cochlea:
    • Meningitus
    • Autoimmune disease
    • AIDS and HIV in certain cases
  • Mumps
  • People (Adults and children) with kidney problems are more susceptible to hearing problems
  • Ménière disease, which affects both hearing and balance. Usually it is associated with tinnitus and has a gradual onset, often resulting progressively in deafness and in certain cases vertigo.
  • Certain prescription drugs which damage the nerves required for hearing will affect hearing. To damage hearing, generally large doses are required. The drugs which can affect hearing include:
    
    • Antibiotics
    • Non steroidal anti-inflammatory
    • Anti-malarial
    • Diuretics

• Vascular diseases involving blood vessels and excessive blood clotting can affect the auditory system
• Various Infections passed from mother to child, including:
  • Chlamydia
  • Syphilis

• Genetic, inherited (Congenital hearing loss):
  • There are both dominant and recessive genes linked to varying levels of hearing impairment
  • The most common congenital hearing loss is DFNB1 or Connexin 26 Deafness
  • Other common forms include Stickler Sydrome, Waaredenburg Syndrom which are dominant and Pendred Syndrome, Usher Syndrome and Vestibular Aqueduct Syndrome which are recessive

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