Impairments in hearing can happen in either frequency or intensity, or both. Hearing loss severity is based on how well a person can hear the frequencies or intensities most often associated with speech. Severity can be described as mild, moderate, severe, or profound. The term “deaf” is sometimes used to describe someone who has an approximately 90 dB or greater hearing loss or who cannot use hearing to process speech and language information, even with the use of hearing aids. The term “hard of hearing” is sometimes used to describe people who have a less severe hearing loss than deafness.

Causes

Normal hearing requires that all parts of the auditory pathway are working correctly. This pathway includes the external ear, middle ear, inner ear, auditory nerve, and the connection between the auditory nerve and the brain. The exact location and nature of the problem in the auditory pathway determines the type and severity of a person’s hearing loss.

Some causes of hearing loss occur before a baby is born. These include genetic disorders (such as Waardenburg syndrome or Crouzon syndrome) and infections (such as congenital rubella or congenital syphilis).

About half of all cases of hearing loss among children are thought to result from genetic factors. Sometimes these children have a syndrome of which hearing loss is only one feature. However, in most children with hearing loss that is due to a genetic cause, the hearing loss is not part of a syndrome. A variant of the connexin 26 gene is responsible for much of the hearing loss in this latter group of children.

To learn more about a specific genetic condition that you think could cause hearing loss, go to the National Library of Medicine's Genetics Home Reference Web site. Information about each genetic condition includes symptoms, how common it is, related genes, treatments, and links to resources where you can learn more about the condition. The Genetics Home Reference also can help you learn more about genetics, including genetic testing, genetic counseling, and gene therapy.

Problems during or soon after birth can also be risk factors for developing hearing loss. These include hypoxia (where the baby does get not enough oxygen), bleeding in the brain, and hyperbilirubinemia (severe jaundice). Children who are born early or at low birth weight are more likely to have problems that may lead to hearing loss. However, children who are normal birth weight can have hearing loss.

Hearing loss can also occur later in a child’s or adult’s life. Causes during this time include infection (such as meningitis, chronic middle ear infections, or measles), injuries (such as head injury), or certain drugs (such as the antibiotic gentamicin). High noise levels (such as from firecrackers or loud rock concerts) can also damage a person’s hearing. About 30 million workers are exposed to dangerous noise levels on their jobs. Another nine million are at risk of hearing loss as a result of working with certain metals or solvents.

Risk Factors

Genetic pre-disposition towards hearing impairment and being within an environment with extended, loud sounds such as a factory for an extended period of time.

Symptoms

Having trouble hearing or comprehending others or the environment around them.

Diagnosis

Hearing loss can affect a child’s potential to develop speech, language, and social skills. The earlier a child who is deaf or hard of hearing starts getting services, the more likely the child’s speech, language, and social skills will reach their full potential.

All newborns should be screened for hearing loss. More and more hospitals are screening babies before they go home. Universal newborn hearing screening programs have three main goals:

• Babies should be screened before they leave the hospital or before 1 month of age.

• If a baby does not pass the screening, he or she should get a follow-up evaluation before 3 months.

• Babies who are deaf or hard of hearing should receive services before they are 6 months old. These services help babies develop speech, language, and social skills.

Prevention

Some causes of hearing loss can be prevented. For example, vaccines can prevent certain infections, such as H-flu meningitis or measles, that can cause hearing loss. Another cause that can be prevented is kernicterus, a kind of brain damage that happens when a newborn baby has too much jaundice. Kernicterus can be prevented by using special lights (phototherapy) or other therapies to treat babies with jaundice. For adults, wearing hearing plugs or avoiding loud environments is the best way to prevent acquiring hearing impairments.

References

Batshaw ML. Children with disabilities (4th edition). Baltimore (MD): Paul H. Brookes Publishing Co.; 1997.

Kenneson A, Van Naarden Braun K, Boyle C. GJB2 (connexin 26) variants and nonsyndromic sensorineural hearing loss (HuGE Review) [Web page]. August 2002 [cited 26 January 2004]. Available from: URL: http://www.cdc.gov/genomics/hugenet/reviews/GJB2.htm.

National Institute for Occupational Safety and Health. Hearing loss prevention [Web page]. [cited 26 January 2004].  Available from: URL: http://www.cdc.gov/niosh/topics/noise/default.html.

Steinberg A, Bain LJ. Hearing loss. In: Batshaw ML, editor. When your child has a disability. Baltimore, (MD): Paul H. Brookes Publishing Co.; 2001. p. 289-306.

Van Naarden K, Decouflé P. Relative and attributable risks for moderate to profound bilateral sensorineural hearing impairment associated with lower birth weight in children 3 to 10 years old. Pediatrics 1999;104:905-10.