You take your dog to the veterinarian because the ear smells bad again. Your dog shakes their head, scratches at the ear, and perhaps you can already see the familiar redness or discharge. If this has happened before, you may feel fairly certain that you already know what comes next: another ear infection and another round of ear medication.
Then your veterinarian starts asking questions that may seem to wander surprisingly far from the ear.
When did this start? Has it happened before? Does your dog lick or chew their feet? Does the skin itch anywhere else? Does the problem occur during a particular season? Does your dog swim? Did the previous treatment completely resolve the problem, and how long did the improvement last?
Your veterinarian may also collect some of the material from the ear and examine it under a microscope rather than simply reaching for an ear medication. Depending upon what they find, they may recommend additional testing, a culture, more extensive cleaning, or investigation into something that at first glance seems unrelated to the ear.
Why go through all of this when everyone can see that the ear looks infected?
Because what we see in the ear today may represent the result of a process rather than the beginning of it. Once you understand that distinction, the veterinarian’s approach to recurring ear disease starts to make much more sense.
The Infection May Not Tell Us Where the Problem Started
One of the most useful things a pet owner can understand about ear disease involves the difference between what started the problem and what developed because of it.
Yeast and bacteria certainly matter. They can contribute to odor, discharge, inflammation, itching, pain, and many of the changes that finally get our attention. We need to identify and address them, but finding yeast or bacteria doesn't necessarily explain why they gained an opportunity to overgrow.
Something may have changed the environment inside the ear first.
Allergies provide a common example. An allergic dog may develop inflammation in the skin lining the ear canal just as inflammation may develop elsewhere on the body. Other dogs may develop ear inflammation associated with endocrine disease, parasites such as ear mites, foreign material, or other underlying conditions.
Once inflammation changes the environment of the ear, moisture, wax, debris, swelling, and changes within the skin can make it easier for a secondary infection to develop.
Now we can see why treating the yeast or bacteria may clear the infection without necessarily solving the entire problem. If we never identify what created the unhealthy ear environment, the conditions that allowed the infection to develop may remain.
Why One Dog Keeps Getting Ear Infections While Another Doesn't
Another part of the picture involves the individual dog. Some dogs enter the situation with factors that make their ears more vulnerable to problems.
Consider a dog who spends much of the summer swimming. Repeated moisture in the ear canal may make secondary problems easier to develop. Another dog may naturally have narrow ear canals. Excessive hair or something physically obstructing the canal, such as a polyp or growth, can also affect the environment within the ear.
Veterinarians call these predisposing factors. They don't necessarily cause an ear infection on their own, but they may increase the likelihood that one develops or make recurring problems more difficult to control.
This distinction matters because two dogs with yeast in their ears may need very different long-term plans. If one struggles primarily with underlying allergy and another repeatedly traps moisture after swimming, treating both dogs as though “yeast equals the problem” misses an important part of what their ears tell us.
The organism matters, but so does the environment in which it grows.
Chronic Inflammation Can Begin to Change the Ear Itself
This part often surprises pet owners because repeated inflammation doesn't simply cause another uncomfortable episode. Over time, it can actually change how the ear functions.
A healthy ear possesses mechanisms that help move normal debris outward. Chronic inflammation can interfere with that process, allowing debris to accumulate more easily. The tissues may swell and thicken, and the canal can gradually narrow.
As those changes progress, normal ventilation decreases and medication may no longer travel easily through the canal. More material becomes trapped, creating an environment that encourages another infection. That infection produces more inflammation, which can cause additional changes within the ear.
At this point, we no longer deal only with whatever triggered the first episode. The changes within the ear itself now help keep the cycle going.
Veterinarians call these perpetuating factors because they allow the disease process to continue. In advanced cases, chronic inflammation may leave the canal severely narrowed or even calcified, making medical treatment increasingly difficult.
This helps explain why a dog who seems to experience “one ear infection after another” may not experience a series of completely separate infections at all. We may instead see repeated episodes of a disease process that never completely resolved.
Putting the Pieces Together
Veterinary dermatologists often organize this investigation into four categories: primary causes, secondary causes, predisposing factors, and perpetuating factors. You don't need to memorize those terms, but understanding what they mean can make your dog's treatment plan much easier to follow.
The primary cause helps explain what started the inflammation. The secondary cause often includes the yeast or bacteria that took advantage of the changed environment. Predisposing factors help us understand why this particular dog or ear may develop trouble more easily, while perpetuating factors describe changes that now help keep the problem going.
Rather than treating these as four unrelated problems, your veterinarian looks at how they interact. A dog may begin with allergic inflammation, develop a secondary yeast infection, possess naturally narrow canals, and eventually develop thickening within those canals after repeated episodes. Treating the yeast addresses one important part of that dog's problem, but it doesn't address everything contributing to it.
Looking at all four pieces gives your veterinarian a way to work through the problem rather than assuming every red, itchy ear needs the same treatment.
That Little Microscope Slide Gives Us Important Information
When your veterinarian places a swab into the ear, rolls the material onto a glass slide, stains it, and looks under the microscope, they perform a test called cytology.
This relatively simple test gives us valuable information because we cannot reliably identify what grows in an ear simply by looking at the color of the discharge or smelling it. Cytology allows us to see yeast, different shapes of bacteria, and inflammatory cells that may help us understand what happens inside the ear.
What we find under the microscope helps guide treatment rather than leaving us to guess from the appearance of the ear alone.
It also explains why automatically reaching for whatever ear medication worked last time doesn't always make sense. Today's ear may not look the same under the microscope as it did during the previous episode. We want to treat what we find today while still considering the larger pattern that brought your dog back.
What About an Ear Culture?
Pet owners sometimes wonder why a veterinarian performs a culture in one case but not another.
Cytology and culture give us different kinds of information, and not every uncomplicated ear infection needs a culture. Your veterinarian may recommend one when certain bacteria appear under the microscope, when several types of bacteria occur together, when the ear doesn't improve as expected with treatment, or when we become concerned that infection may extend into the middle ear.
The history, examination, and cytology help us decide whether we need to investigate further. We don't need to run every possible test on every ear. We want to gather enough information to know which question we need to answer next.
Why Cleaning the Ear Matters
Cleaning may seem like the simplest part of treating an ear problem, but it serves an important purpose.
An inflamed ear may contain wax, inflammatory material, microorganisms, and other debris. Some infections also produce biofilm, which can make successful treatment more challenging. An appropriate ear cleanser helps remove this material and creates a better environment for the ear to recover and for prescribed medication to reach the tissues where we need it.
That doesn't mean every red or painful ear needs vigorous cleaning at home. Before putting products into a significantly inflamed ear, we need to consider what the canal looks like and, when possible, whether the eardrum remains intact. Severe inflammation, obstruction, foreign material, or a damaged eardrum can change the treatment plan considerably.
Sometimes the first step doesn't involve deciding what to put into the ear. We first need to understand what happens inside it.
Why Your Dog's Treatment May Look Completely Different From Another Dog's
Imagine several dogs sitting in the veterinary waiting room, all shaking their heads.
One may struggle with an allergy that repeatedly inflames the ears. Another may develop problems following frequent swimming. Another may carry foreign material deep within one ear. A fourth may show years of inflammation that left the canal thickened and narrowed, while another may have a polyp or growth interfering with the normal ear canal.
From the waiting room, they may all look like dogs with ear infections. Once we examine them and start putting together their histories and findings, however, they tell very different stories.
That explains why one perfect ear medication or treatment plan doesn't exist for every dog. We need to address the individual ear, the individual dog, and the factors contributing to the problem rather than simply treating the symptom they share.
Why Does My Veterinarian Want a Recheck When the Ear Looks Better?
Perhaps your dog's ear looks much better after treatment. The odor disappears, the scratching stops, the discharge clears, and your dog finally seems comfortable again. It can feel strange when your veterinarian still wants to examine the ear another time.
What you can see at home tells us something important, but it doesn't always tell us whether the problem completely resolved deeper within the canal. A recheck allows us to look again, repeat cytology when appropriate, and determine whether infection or inflammation remains before stopping treatment.
The recheck also gives us another opportunity to return to the question that started this entire discussion: Did we address what started the problem, or did we only clear the infection that developed afterward?
That distinction matters even more when a dog struggles with recurring ear problems.
This Is What I Mean by Thinking Like a Veterinarian
When I encourage pet owners to learn how to think like a veterinarian, I’m not asking you to diagnose your dog’s ear disease. I want you to understand why we ask questions that sometimes seem unrelated to the ear itself.
The head shaking, odor, redness, what we see through the otoscope, and what appears under the microscope all give us useful information. But the history around the ear problem often tells us just as much. A dog who started licking the feet weeks before the ear problem appeared may lead us to think differently than a dog who develops trouble after every weekend at the lake. A dog whose ears flare during the same season each year gives us another pattern to consider, while repeated trouble in only one ear may push us to look more closely for something affecting that particular side.
Even the response to previous treatment becomes part of the story. If medication clears the infection but the problem returns a few weeks later, I want to know whether we truly addressed what set the process in motion or whether we only quieted the secondary infection for a time.
This kind of observation helps us move beyond the obvious symptom. We gather the history, look for patterns, compare what changed over time, and then use those connections to decide what question needs an answer next.
You don’t need to walk into the veterinary office already knowing what caused the problem. What helps most is noticing when things changed, what else changed around the same time, whether the problem follows a pattern, and what seems to make it better or bring it back. Those details often give us the clues we need to look in the right direction.
Want to Learn More About How Veterinarians Think?
If this way of looking at your dog's ear feels different from simply treating an infection, that’s exactly why I created my How to Think Like a Veterinarian video series.
In Part 2, we take that thinking farther and look at how seemingly separate clues begin forming patterns.
Together, these videos can help you become a more informed observer and partner in your pet's care—not by teaching you to diagnose your pet, but by helping you recognize the information that may matter when you talk with your veterinarian.
Keep Learning With Me
If you enjoy understanding the why behind your pet's health, join me for Furry Friend Friday Wellness Tips. We explore practical observations you can make at home and the connections that may help you better understand your pet's skin, ears, digestion, behavior, movement, and overall wellness.
The goal doesn't involve turning pet owners into veterinarians. It involves helping you notice more, understand more, and bring better information into the conversation about your pet.
OBSERVE • DISCOVER • THRIVE
Educational Disclaimer
This article provides general educational information for pet owners and does not replace veterinary examination, diagnosis, treatment, or individualized medical advice. Ear disease can result from many different causes, and treatment that works for one animal or one episode may not provide appropriate or safe treatment for another. Painful, persistent, recurrent, foul-smelling, swollen, or discharging ears warrant veterinary evaluation. Changes involving balance, hearing, the eyes or face, significant pain, or other neurologic signs require prompt veterinary attention. Do not place medications, essential oils, home remedies, cleaners, or other products into an abnormal or painful ear without veterinary guidance, particularly when the condition of the eardrum remains unknown.
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