Noise exposure and intense sounds can cause hearing loss. Dr T M Nagaraj explains the other causes of deafness and its symptoms in young children
Noise is a disturbance to the human environment that is escalating at such a high rate that it will become a major threat to the quality of human lives. In the past thirty years, noise, especially in urban areas, has been increasing rapidly. There are numerous effects on the human environment due to the increase in noise pollution.
Noise exposure and intense sounds can cause two main types of hearing loss, namely temporary threshold shift and permanent threshold shift.
Temporary threshold shift is mostly experienced as a temporary dullness in your hearing after exposure to loud noises. Your hearing will subsequently recover — depending on how loud the noises have been and how long you have been exposed to them.
Permanent threshold shift is first experienced 48 hours after exposure to excessive noise. Permanent threshold shift can occur if you have been regularly exposed to excessive noise for long periods of time.Permanent threshold shift hearing loss will normally continue to increase for up to five years after exposure to the noise.
Exposure to noise and high sound levels can also result in tinnitus — a constant sound in your ears or head.
Noise induced hearing loss
NIHL can be caused by a one-time exposure to loud sound as well as by repeated exposure to sounds at various loudness levels over an extended period of time. The loudness of sound is measured in units called decibels. For example, normal conversation is approximately 60 decibels, the humming of a refrigerator is 40 decibels, and heavy city traffic noise can be 85 decibels. Examples of sources of loud noises that cause NIHL are motorcycles, firecrackers, and firearms, all emitting sounds from 120 to 150 decibels. Sounds of less than 80 decibels, even after long exposure, are unlikely to cause hearing loss.
Exposure to harmful sounds causes damage to the sensitive hair cells of the inner ear as well as the hearing nerve. These structures can be injured by two kinds of noise: loud impulse noise, such as an explosion, or loud continuous noise, such as that generated in a woodworking shop.
Hearing loss in infants
In the initial years of coming into the world, the sense of hearing is a critical part of the social and emotional life of a child. It also effects the cognitive development of an infant.
Hearing loss is a hidden disability; that is why it is so important to have your infant’s hearing tested. Each year, more than 4,000 babies are born with hearing loss. Most infants born with hearing problems are otherwise healthy and have no family history of hearing loss. It is important for you to be sure that your infant has normal hearing. It is unlikely that your child will have a hearing loss; however, the only way to know is to have your child’s hearing tested as early as possible. The first year of life is critical to the development of normal speech and language.
A hearing screening with a new born child is a simple method of checking if a baby’s hearing is intact. It is done by sophisticated instruments that will not affect the baby. Good hearing is essential to the social and intellectual development of infants and young children. An audiologist can identify hearing loss in children of any age.
Hearing loss can occur if a child
* Was born prematurely
* Stayed in the neonatal intensive care unit
* Had high bilirubin requiring a transfusion
* Was given medications that can lead to hearing loss
* Has a family history of childhood hearing loss
* Had complications at birth
* Had frequent ear infections; had infections such as meningitis or cytomegalovirus
* Exposed to very loud sounds or noises even of brief duration
When hearing should be evaluated
Most children who are born with a hearing loss can be diagnosed through a hearing screening. But in some cases, the hearing loss is caused by things like infections, trauma, and damaging noise levels, and the problem doesn’t emerge until later in childhood. So it is important to have an infant’s hearing evaluated regularly in the course of their growth.
Children who seem to have normal hearing should continue to have their hearing evaluated at regular doctors’ appointments. Hearing tests are usually done at ages between 4, 5, 6, 8, 10, 12, 15, and 18 and any other time if there is a concern.
But if your child seems to have trouble in hearing, if speech development seems abnormal or if your child’s speech is difficult to understand then the situation implies a serious consultation with your doctor.
Symptoms of a hearing loss
Even if your newborn passes the hearing screening, you should continue to keep an eye on the child to check that his or her hearing is normal.
Some hearing milestones your child should reach in the first year of life:
*Most newborn infants startle or ‘jump’ to sudden loud noises
* By three months, a baby usually recognise a parent’s voice
* By six months, an infant can usually turn his or her eyes or head towards a sound
* By 12 months, a child can usually imitate some sounds and produce a few words, such as ‘mama’ or ‘bye-bye’
As your baby grows into a toddler, signs of a hearing loss may include:
* Limited, poor, or no speech
* Frequent inattentiveness
* Difficulty in learning
* Trying to increase the volume of the TV set
* Failing to respond to conversation-level speech or answers inappropriately to speech
(The writer is HOD - ENT Department, Raja Rajeswari Medical College and Hospital.)
