What Are the Causes of Deafness in Dogs?

Blocked ear canals can result in deafness from the blockage itself or from a secondary infection. This condition is most common in breeds with narrow ear canals and coarse, wiry hair (poodles and some spaniels). When wax, debris, hair or a foreign object lodged in the ear canal blocks your pup's ability to hear, this deafness will disappear upon removal of the object. But foreign objects can wound the ear and debris can create a cozy bed for microbes to grow. The resultant infections can destroy nerves and other tissues, leading to permanent hearing loss. A veterinarian can remove ear debris and prescribe antibiotics or antifungals to treat ear infections.

Hunting dogs are prone to deafness from noise trauma, the result of shotgun blasts close to their sensitive ears. Police and rescue dogs regularly exposed to sirens and other loud noises can also suffer this damage. Noise damage is usually cumulative, like deafness from presbycusis, a fancy name for loss of hearing due to age, and a catchall term for deafness that gradually develops over an animal's (or person's) lifetime. Age-related hearing loss can be related to overt noise trauma, or the result of many small assaults to the inner ear sustained over a lifetime. It can also result from circulatory problems—sensory nerve cells in the ear die off when the blood supply is shunted away from them.

Some breeds and color patterns are known for deafness. The dalmatian is the most famously deafness-prone breed, but beagles, bull terriers, collies, sheepdogs and any breed or individual with a piebald coat (black or brown and white) or a merle coat (one with light and dark shades of a single color) are susceptible to hereditary deafness. White individuals from breeds that usually have dark coats are also prone to deafness. There does not appear to be a "deafness gene" per se; rather, deafness is one side effect of several genotypes that control pigment.

The ultimate cause of pigment-related deafness is not fully understood, but the Deaf Dog Education Action Fund says, "If there is unpigmented skin in the inner ear, the nerve endings atrophy and die off in the first few weeks of the puppy's life, resulting in deafness." Puppies may also be born deaf, which is most common in white or merle-patterned individuals.

Sudden deafness is a fairly rare side effect of several drugs. Aminoglycoside antibiotics (many of the "mycins") can kill off the cochlear hairs, the tissues that allow the ear to sense air vibrations as sound. General anesthesia can also cause deafness. The reason is not fully understood, but doctors speculate that this is the result of a sudden drop in blood pressure that deprives inner ear nerves of oxygen.

Finally, some cases of hearing loss are related to consumption of aspirin (one of the few human painkillers considered safe for dogs). This is also not completely understood, but may be related to circulation. Aspirin-related hearing loss is usually classified as presbycusis and is cumulative. All drug-related deafness is considered permanent.