Hearing loss is either congenital (present at birth or shortly thereafter) or acquired (occurs sometime after birth). In some cases, it is the result of malformation of or damage to a child’s ear that is present at birth. Genetic factors are responsible for about one-half of all cases of hearing loss in children, according to the Centers for Disease Control and Prevention (CDC).

In other cases, an illness or injury damages a child’s hearing sometime after birth. Illnesses that may cause hearing loss include excessive buildup of fluid in the middle ear, infections such as meningitis and ear infections (which usually cause only temporary hearing loss).

Ear infections (e.g., otitis media) are a major source of conductive hearing loss in children. This usually occurs when colds, flu or allergies cause fluid to build up in the inner ear, allowing bacteria to grow. About one in 10 children who have fluid buildup will go on to develop an ear infection. Fluid buildup itself can also cause conductive hearing loss, even if an infection is not present. Other sources of conductive hearing loss in children include blockages of the ear due to insertion of foreign objects or buildup of impacted earwax. Damage to a key part of the ear (e.g., eardrum, ear canal) can result in conductive hearing loss. This type of damage can result from sticking an object in the ear, exposure to a sudden and loud noise, sudden changes in air pressure, a head injury or repeated ear infections.

Most forms of sensorineural hearing loss are present at birth. Damage to the inner ear or auditory nerve causes sensorineural hearing loss. Sources of such damage include:

• Complications during pregnancy or birth. An infection (e.g., toxoplasmosis, cytomegalovirus, rubella) or other illness during pregnancy can contribute to improper development of fetal hearing apparatus, which can cause a hearing impairment. Premature birth and low birth weight can contribute to problems that result in hearing impairment. Problems that occur soon after birth can also cause hearing loss, especially when left untreated. These include lack of oxygen (hypoxia), severe jaundice (kernicterus) and bleeding in the brain.
  
  
• Infections, other illnesses or injuries in the child. Certain sicknesses can damage the structures of the inner ear. Such illnesses include recurrent ear infections, meningitis, mumps, measles, rubella, chickenpox, cytomegalovirus and brain tumors. Head injuries can also cause sensorineural hearing loss.
  
  
• Loud noises. Exposure to a sudden loud noise or loud noise over a period of time can damage the hairs of the cochlea, leading to hearing loss. Excessive volume levels when using electronic devices (e.g., iPods, MP3s, CD players) with earphones for more than five minutes each day can result in permanent damage to hearing, according to a new study.
  
  
• Ototoxic medications. Certain medicines including antibiotics and chemotherapy drugs can have adverse effects on the organs or nerves involved in hearing or balance and lead to hearing loss.
  
  
• Unknown sources. In about half of all cases of sensorineural hearing loss, the cause remains uncertain or unknown.

Certain risk factors make a child more susceptible to hearing loss. For example, many types of hearing loss are the result of genetic factors (e.g, Treacher Collins syndrome). Sensorineural hearing loss is particularly likely to involve genetic factors. Parents of a child with this form of hearing loss are at much higher risk for having additional children with sensorineural hearing loss.