There are three basic types of hearing loss: conductive, sensorineural, and mixed.

Conductive hearing loss occurs when sound is not sent easily through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear. Conductive hearing loss makes sounds softer and less easy to hear. This type of hearing loss may be corrected medically or surgically. Some possible causes of conductive hearing loss are:

• Fluid in the middle ear from colds or allergies
• Ear infection (otitis media)
  • Poor eustachian tube function
  • Hole in the eardrum
• Too much earwax (cerumen)
  • Ear infections (sometimes known as ‘Swimmer’s’ ear or external otitis)
  • Foreign body in the ear canal
  • Malformation of the outer ear, ear canal, or middle ear

Sensorineural hearing loss (SNHL) happens when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain. This is the most common type of permanent hearing loss, and often occurs as a result of ageing.

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

Some possible causes of SNHL are:

• Drugs that are toxic to hearing
• Hearing loss that runs in the family (genetic or hereditary)
• Ageing
• Head trauma
  Malformation of the inner ear
• Exposure to loud noise

Mixed hearing loss occurs when a conductive hearing loss happens in combination with an SNHL. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve.

Other terms associated with hearing loss are:

• Bilateral versus unilateral. Bilateral hearing loss means hearing loss in both ears. Unilateral hearing loss (UHL) means that hearing is normal in one ear but there is hearing loss in the other ear. The hearing loss can range from mild to very severe. UHL can occur in both adults and children.

Below are some possible causes of UHL:

• • Hearing loss that runs in the family (genetic or hereditary)
  • An outer, middle, or inner ear abnormality
  • Syndromes such as Down and Usher syndrome
  • Illnesses or infections such as CMV, Rubella
  • Head injury
  • Exposure to loud noise
  • Traumatic brain injury (TBI)
  • Tumours of the brain or nerve of hearing

Some types of hearing loss include

• Symmetrical versus asymmetrical. Symmetrical means the degree and configuration of hearing loss are the same in each ear. Asymmetrical means the degree and configuration are different in each ear.
• Progressive versus sudden hearing loss. Progressive means that hearing loss becomes worse over time. Sudden means that the loss happens quickly. Such a hearing loss requires immediate medical attention to determine its cause and treatment.
• Fluctuating versus stable hearing loss. Fluctuating means hearing loss that changes over time—sometimes getting better, sometimes getting worse. Stable hearing loss does not change over time and remains the same.

Reference; The American Speech-Language-Hearing Association Audiology Series 2019.