Ear infections are very common in dogs, but why do they get them? Let's start with some basic biology.

A normal ear canal has microorganisms that naturally live there, which is known as "flora". Dogs' ears have Malassezia yeast and Staph bacteria that live in harmony. If the balance gets disrupted in any way, one or both can overgrow and cause an infection of the ear canal, known as "otitis externa". Other bacteria can invade the already irritated ear canal and cause a very severe, opportunistic infection.

Causes of Ear Infections

Ear infections can be triggered in many ways, but these four are the most common:

Anatomy:
Dogs with floppy ears get more ear infections. When the flap of the ear (pinna) covers the opening to the ear canal, moisture, dirt and heat get trapped. Yeast love to grow out of control when ears are hot and humid.

Environment:
Swimming and playing out in the rain are huge risk factors for getting ear infections, especially for floppy-eared dogs, because those ears don't dry out on their own. Ear flora really loves to grow in ears filled with pond water. Just drying the ears after a swim can prevent a lot of ear infections.

Food allergies:
It may sound strange, but food allergies are a common cause of recurrent ear infections. Dogs can develop an allergy to anything they are fed, but the most common offenders are meat proteins and grains. If a dog is constantly exposed to allergenic foods, it can disrupt the balance anywhere in the body, including the ears.

Environmental allergies:

Dogs can have allergies to pollens, molds, dust mites -- just about anything in the environment, even human dander. Environmental allergies cause similar problems as food allergies but can vary with seasons.

Detection and Treatment
Head shaking, scratching at the ears, and ear discharge or odor are all signs of an ear infection. Your veterinarian will look at your dog's ears and look at a swab of ear discharge under the microscope to determine what organisms are involved. Different organisms require different medications.

The best way to be sure the infection gets better is to make sure your dog gets the right medicine for his or her infection. Many dogs will also need an ear flush to make sure the discharge gets cleaned out so the medicine can get in to do its work. If your veterinarian sees signs of an opportunistic bacterial infection, he or she will send a culture to the lab. The results will determine the type of bacteria and the appropriate medications since standard antibiotics often will not work.

For more information about canine ear infections, please see our  handout on ear problems.