There are three types of hearing loss:
- Conductive hearing loss occurs when there is an obstruction or malformation in the middle ear that prevents sound from reaching the inner ear, where the nerve cells process it.
- Sensorineural hearing loss occurs in the nerve cells themselves either because of damage to these cells or because of lack of development of the nerve for hearing.
- Mixed hearing loss involves both the middle ear structures and the inner ear structures.
Hearing loss of any type can present at birth or be acquired. Congenital hearing loss, or hearing loss present at birth, may occur for a number of reasons. At times, it is related to abnormal development of the fetus during pregnancy. Conductive hearing loss may be present at birth if the infant has a cleft palate or atresia of the ear. Approximately one half of all congenital sensorineural hearing loss is related to genetic factors. Most often, neither parent has hearing loss. Most genes that cause hearing loss are recessive. A gene called Connexin 26 has been identified as a common cause for congenital sensorineural hearing loss.
Generally, children born with hearing loss have no other health problems. However, a small number of children with hearing loss are affected by a syndrome that causes multiple health or development problems including hearing loss. Some common syndromes that are associated with hearing loss include: Usher’s syndrome and Down syndrome./p>
Some children may be born with hearing loss as a result of infections present during pregnancy including toxoplasmosis, rubella, cytomegalovirus (CMV), herpes or syphilis.
Acquired hearing loss can occur at any time in life for a number of reasons. Often, children and adults experience some temporary conductive hearing loss as a result of otitis media (middle ear infection). Sometimes sensorineural hearing loss occurs during childhood as a result of serious illness or head injury. Adults, too, may experience hearing loss related to illness or injury. Some syndromes cause hearing loss that progresses over time.
Hearing loss may be acquired as a result of exposure to loud sounds, including music, power tools and fireworks. Typically, noise-induced hearing loss occurs with frequent, prolonged exposure to the loud sound. However, it can occur as a result of an isolated incident if the sound is loud enough. This can occur at any age.
Most often, however, acquired sensorineural hearing loss is a result of the aging process. This is known as presbyacusis, a degeneration of the inner ear and other parts of the auditory system. It typically begins to affect adults around age 55-65 years.