What Causes Hearing Loss?

Children can be born with hearing loss or acquire it. Understanding risk factors can help you protect your child.

Your child's ability to hear can be affected by a wide variety of factors, both prenatally and during the first years of life. "Unfortunately, there is no time where we can definitively tell parents 'your child's hearing will always be normal,'" says Cheryl Edwards, an audiologist and interim director of diagnostic audiology at Boston Children's Hospital. But many causes of hearing loss are preventable, so understanding potential risk factors will help you protect your child's hearing and be prepared if a problem does emerge.

Linda Farwell

Congenital Hearing Loss

One to 6 of every 1,000 babies are born without the ability to hear, or with significantly reduced hearing, and in most cases this loss will be permanent. More than 50 percent of all hearing loss is hereditary and due to genetic defects, but unless you have genetic testing, you may not know that you carry a defective gene. That's because about 70 percent of all genetic hearing loss is considered "autosomal recessive," which means both parents pass along a genetic defect to their child, but the gene is recessive so they themselves do not have hearing loss.

A less common form of genetic hearing loss is called "autosomal dominant." This happens when the abnormal gene is dominant in one parent, so it will be active in the baby, even though the other parent's matching gene is normal. That parent may also have hearing loss or signs of symptoms of a genetic syndrome, or both, that raise the likelihood of hearing loss. (Such syndromes include Down syndrome, Usher syndrome, and Treacher Collins syndrome.)

About a quarter of congenital hearing loss is not genetic and caused by a problem during pregnancy or delivery, such as:

- Premature birth
- Low birthweight
- Birth injuries
- Complications resulting from severe cases of jaundice
- Lack of oxygen
- Prenatal exposure to toxins such as drugs or alcohol consumed during pregnancy
- Maternal diabetes
- Toxemia during pregnancy
- Rubella, herpes simplex virus, or another maternal infection

Acquired Hearing Loss

Profound early-onset deafness is present in 4 to 11 per 10,000 children; about 15 percent of children have mild to moderate hearing loss in one or both ears. About 50 percent of those cases are genetic (see above), but the rest are usually the result of illness, injury, or another external factor. Here's a list of the possible culprits.

- Diseases: Severe cases of meningitis, measles, encephalitis, chicken pox, mumps, and the flu can all increase your child's risk for permanent hearing loss. Protect your family by staying up-to-date on all vaccines and getting annual flu shots.

- Ototoxic Medications: More than 200 medications currently on the market are known to be ototoxic, meaning they can cause hearing loss, ringing in the ear, or balance disorders, according to the American Speech-Language-Hearing Association. This side effect occurs when the medications cause damage to sensory cells located in the inner ear; in many cases, the hearing loss and other symptoms are temporary and resolve once medication is stopped, but sometimes the damage is permanent. If a doctor needs to prescribe an ototoxic medication (most are used to treat severe infections, cancer, or heart disease) for your child, he should put a plan in place to evaluate and monitor your child's hearing and balance. Let him know if your child reports a ringing sound in his ears, feels dizzy, or becomes less steady on his feet, as these can be early warning signs of a problem.

- Noise exposure: You might think your kid is too young for noise-related hearing loss--after all, he's not cranking up his iPod or going to rock concerts just yet! But some noisemaking toys are actually loud enough to cause permanent hearing loss or other damage. Many squeaky rubber toys, trucks and cars with horns and sirens, talking dolls, cap guns, and other playthings emit sounds louder than 90 decibels, which is the level at which workers would have to wear ear protection. And if your little one holds the toy directly up to her ear, she may be exposed to 120 decibels--as loud as a jet plane taking off! Avoid buying loud toys and take the batteries out of any noisy toys in your home; the Sight & Hearing Association publishes a list of the noisiest toys each year at sightandhearing.org.

- Head Injuries: If your child experiences a traumatic brain injury for any reason, you'll want to make sure his hearing is evaluated and monitored carefully; temporary or permanent hearing loss, as well as ringing or buzzing in the ears, is a common side effect of this complex condition.

- Ear Infections: Most children will have at least one acute ear infection by the time they are 1 year old, because the passage between their middle ear and the back of their throat is smaller and more horizontal than it is in adults, making it especially prone to infection. Some children experience short-term hearing loss during an ear infection because fluid gets trapped in their middle ear and muffles sound. This usually--but not always--clears up once the fluid resolves, though that fluid can hang around for a few months. If your little one racks up a slew of ear infections (usually three or more infections with fluid by age 3), however, that trapped fluid never has a chance to drain and hearing loss can persist. If you suspect that is happening, ask your pediatrician to refer you to an audiologist for a hearing evaluation and to an otolarynologist (an ear, nose, and throat doctor, or ENT). If the ear infections are especially persistent or don't respond well to antibiotics, your ENT may recommend surgery to put tubes in your child's ears, which should clear up the excess fluid and prevent infections. "The good news is," Edwards says, "once we clear out the excess fluid, whether medically or with surgery, hearing is almost always restored."

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