Dogs get ear infections primarily because of their ear canal shape, which traps moisture, wax, and debris far more easily than a human ear does. Unlike the short, straight human ear canal, a dog’s ear canal is long, narrow, and bends almost 90 degrees before reaching the eardrum. That sharp turn creates a warm, dark pocket where bacteria and yeast can thrive, especially when something disrupts the ear’s normal balance.
The L-Shaped Ear Canal
The single biggest reason dogs are prone to ear infections is anatomy. The canine ear canal drops vertically, then makes a near-right-angle turn horizontally toward the eardrum. Water, wax, and debris that enter the ear don’t drain easily the way they do in a human’s short, mostly straight canal. Instead, material collects at that bend, and the warm, moist environment becomes a breeding ground for microorganisms. This design also makes it harder for air to circulate and dry the canal naturally.
Bacteria and Yeast Already Living in the Ear
The organisms behind most ear infections aren’t invaders from the outside. They’re bacteria and yeast that already live on your dog’s skin in small, harmless numbers. When conditions inside the ear shift (more moisture, more wax, inflammation from allergies), these normal residents multiply out of control. In a large study of dogs with ear infections, about 75% had bacterial overgrowth, most commonly a species of Staphylococcus that naturally colonizes dog skin. Roughly 25% had yeast overgrowth, predominantly a species of Malassezia, a fungus that’s a normal part of the skin’s ecosystem. Many dogs end up with both bacteria and yeast at the same time, which is why vets often prescribe combination treatments.
Moisture and Swimming
Water is one of the most common triggers. When your dog swims, gets bathed, or even walks through heavy rain, water can travel down into that L-shaped canal and get trapped at the bend. The combination of trapped water and the naturally warm, dark ear canal creates ideal conditions for bacteria and yeast to explode in number. This is sometimes called “swimmer’s ear,” and it’s especially common in dogs who swim regularly during summer months.
Cleaning your dog’s ears after they get wet is one of the simplest ways to prevent this. A veterinarian-approved ear cleaner helps dry the canal without disrupting its natural balance. Overcleaning, though, can backfire. For dogs with healthy ears, routine cleaning is only needed when you notice dirt or debris, or after the ears get wet. That typically means every one to two weeks for maintenance, not daily.
Allergies: The Hidden Driver
Allergies are the most underappreciated cause of ear infections in dogs. Environmental allergens (pollen, dust mites, mold) and food sensitivities trigger inflammation inside the ear canal. That inflammation causes the lining to swell and produce excess wax, which feeds the bacteria and yeast already living there. If your dog gets ear infections repeatedly, especially at the same time each year or alongside itchy skin and paws, allergies are a likely underlying cause. Treating only the ear infection without addressing the allergy means it will almost certainly come back.
Ear Mites
Ear mites are tiny parasites that spread through close contact between animals. They’re most common in puppies and dogs that live with cats, since cats carry them frequently. Once mites colonize the ear canal, they cause intense irritation. The ear lining thickens, wax glands go into overdrive, and the canal fills with dark, crumbly debris that looks like coffee grounds. That damaged, inflamed tissue is then vulnerable to secondary bacterial and yeast infections. Ear mites are highly treatable, but the secondary infection they create sometimes outlasts the mites themselves.
Foreign Objects
Grass seeds, particularly foxtails, are a seasonal hazard. These barbed seeds can lodge in the ear canal during walks through tall grass or fields. Because their shape is designed to burrow forward and not come back out, they work deeper into the canal over time. They don’t break down inside the body, so they cause ongoing irritation and eventually infection. If your dog suddenly starts shaking their head, tilting it to one side, or scratching one ear obsessively, a foreign body is a real possibility, especially in late spring and summer. These usually can’t be seen or removed without a vet’s otoscope.
Hormonal Conditions
Dogs with hypothyroidism (an underactive thyroid) are significantly more prone to recurring ear and skin infections. The hormonal imbalance weakens the skin’s natural defenses, making the ear canal less resistant to bacterial and yeast overgrowth. Common signs of hypothyroidism include hair loss along the trunk and tail, a dull or brittle coat, darkened skin, and weight gain. Cushing’s disease, where the body produces too much cortisol, has a similar effect. If your dog has chronic ear infections alongside these other symptoms, a blood test for hormonal conditions is worth pursuing.
Breeds at Highest Risk
Ear shape matters enormously. A large study from the Royal Veterinary College found that dogs with long, floppy ears had roughly 1.8 times the risk of ear infections compared to dogs with upright, pointed ears. Floppy ears act like a lid over the canal, trapping warmth and moisture while blocking airflow. The five breeds most affected were Basset Hounds, Chinese Shar Peis, Labradoodles, Beagles, and Golden Retrievers.
Poodle breeds overall had nearly twice the risk of ear infections compared to non-poodle breeds, likely because of the thick hair that grows inside their ear canals. Spaniel breeds had about 1.24 times the risk. Designer crossbreeds like Labradoodles and Cockapoos had 1.63 times the risk of standard crossbreeds, inheriting the ear traits that make their parent breeds vulnerable.
Dogs with narrow or folded ear canals, like Shar Peis, face a different version of the same problem. Their canals are physically tighter, so even a small amount of inflammation or wax buildup can block airflow completely.
Signs to Watch For
Most ear infections start with subtle changes before becoming obvious. Early signs include your dog scratching at one or both ears more than usual, shaking their head, or rubbing the side of their face against furniture or carpet. As the infection progresses, you may notice redness or swelling at the ear opening, a brown or yellowish discharge, and a noticeable odor. Some dogs become sensitive about having their ears touched or yelp when the ear is bumped. Head tilting, loss of balance, or walking in circles can indicate the infection has moved deeper, past the eardrum into the middle or inner ear.
Preventing Recurring Infections
For dogs prone to ear infections, prevention comes down to managing the underlying cause. If allergies are the trigger, controlling them with appropriate treatment will do more than any amount of ear cleaning. If moisture is the problem, drying the ears after swimming or baths is essential. For breeds with heavy ear flaps, lifting the flaps periodically to let air circulate can help.
Resist the urge to clean too frequently. Overcleaning irritates the ear canal lining and can actually make infections more likely. Cornell University’s veterinary guidance recommends cleaning only when you see visible dirt or after the ears get wet. When you do clean, use a product designed for dogs, since the ear canal has a specific chemical balance that household products can disrupt. Cotton balls work well for the outer canal, but never push anything deep into the ear or use cotton swabs, which can pack debris against the eardrum.