In general terms, there are two types of hearing loss: conductive and sensorineural. In some cases, hearing loss results from a combination of conductive and sensorineural causes, and this is referred to as a mixed hearing loss.
Conductive Hearing Loss
Conductive hearing loss is caused by any condition or disease that blocks or impedes the conveyance of sound through the outer or middle ear. The result is a reduction in the sound intensity (loudness) that reaches the cochlea. Generally, the cause of conductive hearing loss can be identified and treated, resulting in a complete or partial improvement in hearing. Medical treatment may include medication or surgery. Following the completion of medical treatment, hearing aids are effective in correcting the remaining hearing loss. Some examples of causes of conductive hearing loss are: impacted cerumen, atresia (closed ear canal), perforated eardrum, otitis media (fluid in the middle ear), otosclerosis and ear trauma.
Sensorineural Hearing Loss
Sensorineural hearing loss results from inner ear or auditory nerve dysfunction. In many cases, the specific cause cannot be determined. It is typically irreversible and may be progressive. As with conductive hearing loss, this type of loss also reduces the intensity of sound, but it might also result in a distortion of sounds. This distortion can cause a lack of clarity even when sounds, particularly speech, are loud enough. The treatment for sensorineural hearing loss is amplification through hearing aids and other assistive listening devices. Some examples of causes of sensorineural hearing loss are Meniere’s disease, noise exposure, aging (presbycusis), trauma, ototoxic medication, acoustic neuroma, congenital (birth) and hereditary.
Mixed Hearing Loss
Mixed hearing loss results from a combination of conductive and sensorineural causes. The conductive component of the hearing loss may be treatable with medical or surgical intervention, while the sensorineural component often requires amplification to treat.
Hearing loss can be caused by something as simple as excessive ear wax or as complex as a congenital disorder, medical problem or disease.
The main causes of hearing loss are as follows:
- Aging (presbycusis)
- Excessive noise (i.e. construction, rock music, gun shot, etc.)
- Sudden onset
- Injury to the head or ear
- Birth defects or genetics
- Ototoxic reaction to drugs or cancer treatment (i.e. antibiotics, chemotherapy, radiation)
Age-related hearing loss (presbycusis) occurs as a natural result of the aging process. This is a progressive loss as the inner ear (cochlea) and/or other parts of the auditory system degenerate over time, with loss of hearing for the high pitch sounds occurring first. The process may begin as early as age 20, but it is typically not until around ages 55 to 65 that high frequencies in the speech range begin to be affected.
Noise-induced hearing loss can result from prolonged exposure to harmful levels of noise. Prolonged noise exposure damages the hair cells in the cochlea and results in permanent hearing loss. Noise-induced hearing loss usually develops gradually and painlessly. Hearing loss can also occur as a result of an acoustic trauma due to a single exposure or few exposures to very loud sound.
Sudden onset hearing loss occurs across the entire age spectrum with equal prevalence in men and women, but most patients are between 50–60 years of age. More than half also experience tinnitus, aural fullness, and/or vertigo. An estimated 4,000 people will develop sudden sensorineural hearing loss each year in the United States. There are numerous causes for this type of loss, ranging from autoimmune inner ear disease and viral infections to traumatic insult (skull fracture, puncture of the eardrum, sudden changes in air pressure). If treated expeditiously, patients can often recover or stabilize their hearing.
Middle ear infection, or Otitis Media, may cause hearing loss when fluid from the infection builds up behind the eardrum. Sounds are diminished when they pass through the fluid-filled space, and this causes a drop in the perceived loudness. Anyone can get an ear infection, but children are frequently affected. Three out of four children will have at least one ear infection by their third birthday. An untreated ear infection may lead to permanent hearing impairment. It is particularly important to promptly treat middle ear infection in young children, to prevent any delay in speech development.
Hearing loss can result from physical trauma, such as injury to the head or ear. Examples include skull fractures of the temporal bone—the area of the skull just behind the ear; puncture of the eardrum by foreign objects; or sudden changes in air pressure.
Genetic sensorineural hearing loss includes a broad range of disorders that affect infants, children, and adults. Affected individuals may have unilateral or bilateral hearing loss ranging from mild to profound, and the loss may be stable or progressive.
Ototoxic hearing loss occurs when someone takes a drug that has a side effect of damaging the hearing system. Sometimes the drug-induced hearing loss is temporary and can be reversed or stopped. In other cases, it is permanent. People with preexisting hearing loss need to be especially aware of the potential for ototoxic effects, as an ototoxic drug can make an existing hearing loss worse. Ototoxic drugs include some antibiotics, chemotherapy drugs and anti-inflammatory medications, including some over-the-counter drugs.
An Audiologist is a healthcare professional who specializes in identifying, diagnosing, treating and monitoring disorders of the auditory and vestibular system portions of the ear. Audiologists are trained in anatomy and physiology, hearing aids, cochlear implants, electrophysiology, acoustics, neurology, counseling and sign language. Depending on the program they pursue, Audiologists typically graduate with one of the following qualifications: Master’s degree, Doctor of Audiology (AuD), PhD, or Doctor of Science (ScD).
Audiologists perform a wide range of hearing-related services, such as:
- Diagnose, manage and/or treat hearing or balance problems
- Dispense hearing aids and recommend and map cochlear implants
- Counsel patients of all ages—from diagnosing hearing loss in infants to teaching coping and compensation skills to late-deafened adults
- Help design and implement personal and industrial hearing safety programs, newborn hearing screening programs and school hearing screening programs
- Provide custom ear plugs and other hearing protection devices to help prevent hearing loss
- Work as auditory scientists in a research capacity