Hearing loss occurs when something happens to one or more parts of a child’s ear that causes a reduction in the ability to detect or process sounds. The loss of hearing that results may be mild, moderate, severe or profound. At its furthest extreme, hearing loss results in deafness, or total inability to hear sounds.

Problems with hearing are among the most common major abnormalities in infants, according to the American Academy of Pediatrics (AAP). Hearing loss in both ears is present in between one and three out of every 1,000 infants who are born healthy, and in between two and four out of every 100 infants who need intensive care following birth. Hearing impairment is one of the most common forms of birth defects.

People hear through their ears, which help detect sounds in the environment. All sounds have a pitch and intensity (loudness measured in decibels). The process of hearing begins when sounds from the environment travel like waves and are funneled into the outer ear (pinna). The sound travels through the eardrum (the tympanic membrane, which vibrates in response to sound waves) and into the middle ear. There, three small bones (ossicles) – known as the hammer (malleus), anvil (incus) and stirrup (stapes) bones – begin to vibrate, sending the sound signals to the inner ear. A portion of the inner ear called the cochlea is filled with fluid and lined with thousands of tiny hairs. The sound signals move these hairs, which turn the vibrations into electric signals that move along the auditory nerves on their way to the brain.

When something interferes with a child’s ability to process sound, hearing loss may result. In some cases, this damage to a child’s hearing is present at birth. In other cases, a hearing loss does not develop until later in a child’s life.

Hearing loss may involve deficits in detecting a range of pitches (high and low sounds), and/or a range of intensities (loud to soft sounds). Children without hearing impairment can hear sounds in the 0 to 20 decibel hearing level (dBHL) range. Hearing loss is generally diagnosed as belonging to one of the following four categories:

• Mild hearing loss (20 to 40 dBHL). Affects the ability to hear soft sounds. Children who have begun to speak before this type of impairment occurs will likely have normal speech and will be able to engage in conversation relatively easily. Children who have not yet begun to speak at the time of a mild hearing loss may have deficits in speech and language ability that benefit from speech language therapy.
  
  
• Moderate hearing loss (40 to 60 dBHL). Significantly affects the child’s ability to have conversations. Hearing aids and speech therapy can be employed to help children to attend regular schooling and to function well socially.
  
  
• Severe hearing loss (60 to 80 dBHL). Makes normal conversation impossible and significantly impacts a child’s ability to learn spoken language. Children may be able to detect some loud noises and to make out some words, and may benefit from speech and language therapy and hearing aids. Children with severe hearing loss often perform best when attending schools for the deaf.
  
  
• Profound hearing loss (80 or more dBHL). Makes it impossible to hear most sounds, including normal speech. It is extremely difficult for children with profound hearing loss to develop useful spoken language, although children who learn to speak before having a profound hearing loss may be able to retain an understanding of language. Children who have profound hearing loss before learning to speak will not be able to acquire normal language or speech. However, learning sign language will allow them to communicate effectively, and use of a cochlear implant may increase the likelihood that children with profound hearing loss will be able to develop spoken language.