I recently received the following question from a reader:

My cat is only five, but I’ve noticed lately that he doesn’t seem to hear me, ever, and he’s often startled when I come up behind him. Nothing has happened to him that I know of.

How do you know when cats have hearing loss, and can they go deaf from being in loud environments and/or accidents?

Cats are well known for having sensitive hearing. In fact, all of their senses appear to be stronger than ours. Humans, it seems, have evolved to dedicate a large portion of our cognitive resources to managing and understanding the complex social environments in which we live. Cats, as more solitary creatures, have evolved to be phenomenal predators. The result: Cats clear our houses of mice while we read US Weekly.

Can cats go deaf? Absolutely.

In fact, many cats become deaf within months of their birth (all cats technically are born deaf, but most acquire the ability to hear within two weeks). Fortunately, pet cats generally do very well without the ability to hear.

Cats, like humans, hear through their ears. Sound waves move through the air and are captured in the outer ear by the visible portion of the ear (called the pinna), which funnels the waves towards the eardrum. You might have noticed that cats can move each pinna to better hear sounds coming from a certain direction.

The sound waves strike the eardrum, which vibrates in response to them. The vibrations are transmitted through a series of bones in the middle ear that in turn stimulate a structure called the oval window. The oval window transmits the vibrations into a fluid that resides in the inner ear. The movement of this fluid then stimulates special cells involved in hearing. The cells in turn transform the vibrations into electrical impulses that are sent along a nerve to be interpreted by the brain. It is amazing to understand that all of this happens so fast that it seems instantaneous.

A problem with any portion of the system described above — the outer ear, the middle ear, the inner ear, the nerve, or the brain — can cause deafness.

Therefore, there are many causes of deafness in cats. One of the most well known is hereditary deafness in white cats, especially those with blue eyes. This form of deafness is transmitted as a dominant gene, and it causes degeneration of the structures of the inner ear by about five weeks of age. Many other cats are born with improperly formed ear structures that prevent them from ever experiencing sound in the manner that others do. (Note that deaf animals can still experience sound as vibrations striking the body. However, they do not hear the sound in the way that most others do.)

Another common cause of deafness is chronic or severe ear infections, especially if the middle ear is involved. Such infections may lead to permanent damage to the structures that transmit sound waves.

Trauma to the hearing apparatus or to the brain may result in deafness. Accidents absolutely can result in deafness.

Also, some medications (including certain antibiotics and heart medications) have the potential to be “ototoxic” — in other words, they might damage the hearing apparatus. Exposure to certain industrial chemicals can have the same result.

Hearing loss can occur in cats, as in people, as a result of aging. The structures of the inner ear may degenerate with time, leading to progressive deafness.

The structures of the inner ear also are vulnerable to loud noises, especially if they occur over an extended period of time. Kittens and cats who are exposed to loud environments are at risk hearing loss.

Finally, especially in older cats (unlike Ambrose), tumors in the ear or brain may cause deafness.

The most common symptom of deafness in cats is exactly what my reader described: Deaf cats seem to startle easily when approached because they can’t hear the person coming. They also might be difficult to rouse from sleep. Such cats must be handled carefully, because startled cats may instinctively scratch or bite first and ask questions later.

Other signs of feline deafness include very loud vocalization and rough play with other cats (because they can’t hear distress cries that indicate pain in their playmates).

People who wonder whether their cats are deaf should know it’s possible to test for deafness in cats. The BAER (short for brain stem auditory evoked response) test can objectively measure hearing in pets. The test is performed only at special centers. It involves placing electrodes on a cat’s skull and then stimulating each ear individually with noises while the other ear is fed white noise to isolate it. A list of centers that perform BAER testing can be found here.

Of course, for many cat owners, BAER testing would provide strictly academic information. From a practical standpoint, deafness in cats is not a big deal. Many people who cannot hear do not consider themselves handicapped at all, despite the fact that for us hearing is second only to eyesight in importance among our senses.

For cats, the nose trumps all other sensory organs in importance. Eyesight likely is second, and hearing may be third (although tactile stimulation — such as that received by the whiskers — is also a contender for third place).

Deaf cats should be seen by a vet to ensure that they do not have a progressive pathological process, and to ensure that they don’t have a problem such as an ear infection that is causing pain. Otherwise they require only two lifestyle adjustments. They should not be allowed outside, because they will be more vulnerable to predation and trauma. Also, their owners shouldn’t sneak up on them. That is all.

Read more on cats and health:

• 5 Things I Did Wrong When I Took My Cat to the Vet
• Has Your Cat Ever Given Your Vet a Funny Story?
• 11 Cat Emergencies That Need Immediate Veterinary Attention

Got a question for Dr. Barchas? Ask our vet in the comments below and your topic might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)