Otitis externa is inflammation of a dog’s external ear canal, stretching from the outer ear opening down to the eardrum. It’s one of the most common reasons dogs end up at the vet, affecting an estimated 10 to 20 percent of the dog population. The condition ranges from a mild, itchy nuisance to a painful, recurring problem that can permanently damage the ear if left untreated.
What Happens Inside the Ear
A dog’s ear canal is L-shaped, dropping vertically and then turning horizontally toward the eardrum. This shape is great for funneling sound but terrible for draining moisture and debris. When the lining of this canal becomes inflamed, it swells, traps warmth and moisture, and creates the perfect environment for bacteria and yeast to multiply. The outer ear flap may or may not be involved.
The inflammation itself is usually a reaction to something else. Otitis externa is rarely a standalone disease. It’s better understood as the ear’s response to an underlying trigger, with infection piling on as a secondary problem.
Common Causes
Allergies are the single most frequent driver. Dogs with environmental allergies (pollen, dust mites) or food sensitivities often develop ear inflammation as one of their first symptoms. The allergic reaction causes the ear canal lining to swell and overproduce wax, which then feeds opportunistic microbes.
Other primary causes include ear mites (tiny parasites that live in the canal), foreign objects like grass seeds lodged in the ear, and excess moisture from swimming or bathing. Middle ear infections can also spread outward and trigger inflammation in the external canal.
Once the ear environment is disrupted, bacteria and yeast move in fast. The most common bacterial culprit is a staph species called Staphylococcus pseudintermedius, found in roughly a third of infected ears in one large study. On the yeast side, Malassezia pachydermatis dominates, accounting for about two-thirds of yeast isolates. These organisms live on healthy dog skin in small numbers but explode when conditions shift in their favor.
Signs to Watch For
The earliest and most obvious sign is scratching or pawing at one or both ears. You might notice your dog shaking their head frequently, tilting it to one side, or rubbing their ear against furniture or the floor. The ear may smell unusually strong, sometimes sweet and yeasty, sometimes foul.
Look inside the ear flap. Redness, swelling, and discharge are hallmarks. The discharge can range from dark brown and waxy (common with yeast) to yellow or greenish (more typical of bacterial infections). In painful cases, dogs may flinch, whimper, or pull away when you touch the ear. Some dogs become irritable or reluctant to eat on the affected side.
Which Breeds Are Most at Risk
Ear shape matters enormously. Dogs with long, droopy ear flaps have nearly twice the risk of ear infection compared to dogs with erect, pointy ears. The flap acts like a lid, trapping humidity and reducing airflow inside the canal.
Research from the Royal Veterinary College identified the five most affected breeds: Basset Hounds, Chinese Shar Peis, Labradoodles, Beagles, and Golden Retrievers. Poodle breeds overall had 1.91 times the risk compared to non-poodle breeds, and spaniel breeds had 1.24 times the risk. Designer crossbreeds like Labradoodles and Cockapoos carried 1.63 times the risk of standard crossbreds, likely inheriting the dense ear canal hair and floppy ears of their parent breeds.
That said, any dog can develop otitis externa. Short-eared breeds simply do so less often.
How Vets Diagnose It
Your vet will start by observing your dog’s head carriage and ear posture from a distance, checking for asymmetry, head tilting, or signs of facial nerve problems. Then they’ll examine the canal using an otoscope, a lighted instrument with a cone-shaped tip. This lets them see down the vertical and horizontal portions of the canal, check for foreign bodies, assess how swollen the canal walls are, and evaluate the eardrum.
A sample of ear discharge is typically examined under a microscope (called cytology) to identify whether bacteria, yeast, or mites are present. This step matters because the type of organism changes the treatment approach. For chronic cases, infections that keep coming back, or inflammation in only one ear, your vet may recommend allergy testing, skin biopsies, or imaging to find the deeper cause.
Treatment and What to Expect
Treatment targets two things at once: the infection in the ear and the underlying cause that triggered it. Most cases start with a thorough professional ear cleaning to remove built-up debris, followed by topical ear medication you’ll apply at home. These products typically combine an ingredient to fight bacteria, one to fight yeast, and a steroid to reduce swelling and pain.
Some newer formulations are long-acting, applied once at the vet’s office and designed to work for one to two weeks without daily home treatment. This is particularly helpful for dogs that resist having their ears handled. For severe or deep-seated infections, oral medications may be added.
One thing worth knowing: the steroid component in ear medications can occasionally affect your dog’s adrenal system, especially with prolonged use. If your dog needs extended treatment, your vet may monitor for this. Mild cases often resolve within two to three weeks. Chronic or allergy-driven cases require longer management plans and sometimes lifelong maintenance to keep flare-ups under control.
Cleaning Your Dog’s Ears at Home
Proper ear cleaning supports treatment and helps prevent recurrence. Cornell University’s veterinary college recommends this approach: fill the ear canal with a veterinary ear cleaning solution, gently massage the base of the ear for about 30 seconds, and then let your dog shake their head (have a towel ready). After the shake, use cotton pads or cotton balls to wipe away loosened debris. Only go as deep as your finger fits comfortably, about one knuckle in, and work from the inside outward.
A few important rules: never use cotton swabs, which push debris deeper and risk damaging the canal. Don’t force cleaning solution into the ear with a hard squeeze, as the pressure can rupture the eardrum. Avoid anything containing alcohol or hydrogen peroxide, both of which irritate inflamed tissue.
Preventing Recurrence
If your dog swims regularly, moisture control is critical. Drying ear drops used after swimming can help prevent the warm, wet conditions that bacteria and yeast thrive in. Dogs with allergy-driven ear problems often benefit from routine ear flushes during high-pollen seasons, combined with broader allergy management like immunotherapy or dietary changes.
For floppy-eared breeds, periodic cleaning on a schedule your vet recommends (often every one to two weeks) keeps wax and moisture from building up. Over-cleaning can also irritate the canal, though, so frequency should match your dog’s individual needs rather than a one-size-fits-all rule.
What Happens If It Goes Untreated
Repeated or neglected ear infections cause the canal walls to thicken and scar over time. The canal gradually narrows, a process called stenosis, which makes future infections even harder to treat because medication can’t reach the deeper portions. In advanced cases, the canal can calcify and become rigid. At that point, the only option may be surgery to remove the ear canal entirely. Infection can also spread inward to the middle and inner ear, causing hearing loss, balance problems, or chronic pain. Early and consistent treatment avoids these outcomes in the vast majority of dogs.