A dog with an ear infection will typically have a red, swollen ear canal with visible discharge that ranges from yellow to reddish-brown or dark brown, depending on the type of infection. But the visual signs are only part of the picture. Most owners first notice behavioral changes, like persistent scratching or head shaking, before they ever look inside the ear.
What You’ll See Inside the Ear
The most obvious sign is discharge. A waxy, yellow, or reddish-brown buildup in and around the ear canal points to infection. The color and consistency give clues about what’s going on. Yeast infections tend to produce a dark brown, greasy discharge, while bacterial infections often cause a yellowish or greenish pus-like fluid. In either case, you may also notice the inner ear flap and canal entrance looking red, inflamed, or visibly swollen compared to the healthy ear.
In more advanced or chronic infections, the ear canal itself can narrow from ongoing swelling and tissue thickening. If you lift your dog’s ear flap and the canal opening looks puffy or partially closed off, the infection has likely been progressing for a while. You might also see crusting or scabbing around the ear opening, especially if your dog has been scratching.
How It Smells
Smell is one of the most reliable indicators, and it’s often what prompts owners to check the ears in the first place. Yeast infections produce a distinct musty, sweet odor, sometimes compared to bread or corn chips. Bacterial infections smell different: more foul, sharp, and unpleasant. If your dog’s ear smells noticeably bad from even a short distance, infection is very likely.
Behavioral Signs to Watch For
Dogs can’t tell you their ear hurts, but their behavior makes it fairly obvious. The most common signs include frequent scratching at the affected ear, repeated head shaking, and holding the head tilted to one side. Some dogs cry or whimper when they scratch, which signals real pain. You might notice your dog pulling away or yelping when you touch the ear or the area around it.
In more severe cases, dogs scratch so intensely that they create visible scratch marks or open sores on the skin around their ear and face. This secondary trauma is a sign the infection has worsened and is causing significant discomfort.
What Causes Ear Infections in Dogs
Allergies are the single biggest driver. They’re involved in up to 43% of ear infection cases, and ear infections occur in 65% to 80% of dogs with food allergies. Environmental allergens, like pollen or dust mites, can trigger the same cycle of inflammation and infection.
Moisture is another major factor. Dogs that swim frequently or get water in their ears during baths are more prone to infections because the damp environment encourages bacterial and yeast growth. Breeds with large, floppy, or hairy ears, like cocker spaniels, miniature poodles, and Old English sheepdogs, face higher risk because their ear shape traps moisture and reduces airflow. Ear mites can also create conditions that lead to secondary bacterial or yeast infections.
Hormonal conditions like an underactive thyroid can contribute to repeated infections as well. In some cases, the cause is a foreign body, polyp, or tumor inside the ear canal, which won’t resolve with medication alone.
Yeast vs. Bacterial Infections
These are the two main types, and they look and smell somewhat different. Yeast infections produce that dark brown, waxy discharge with a musty, sweet smell. Bacterial infections are more likely to show yellow or greenish discharge with a sharper, more foul odor. Some dogs have both at the same time.
A vet can tell the difference definitively by taking an ear swab and examining it under a microscope. The most common yeast involved is a peanut-shaped organism that’s easy to identify on a slide. Bacterial infections are categorized by the shape of the bacteria: round bacteria (cocci) are usually easier to treat, while rod-shaped bacteria can be more stubborn and may require targeted treatment.
When an Ear Infection Becomes Serious
Most ear infections start in the outer ear canal. Left untreated, they can push deeper into the middle and inner ear, where the consequences become more serious. A dog with a deep ear infection may walk with an unsteady, almost drunken gait, keep its head persistently tilted to one side, or show rapid, jerking eye movements. These are signs of vestibular disruption, meaning the infection has affected the structures responsible for balance. Some dogs become reluctant to stand or walk at all and tend to lean or fall in the direction their head is tilted.
Another common complication is an aural hematoma, a blood-filled swelling in the ear flap caused by all that vigorous head shaking and scratching. The ear flap becomes thick, spongy, and puffy, sometimes swelling to the size of a small pillow. Dogs often hold the affected ear slightly away from their head because of the discomfort. If left untreated, the hematoma can eventually be reabsorbed by the body, but the resulting scar tissue distorts the ear into a wrinkled, cauliflower-like shape that can actually obstruct the ear canal and make future infections more likely.
What to Expect at the Vet
The vet will look inside the ear canal with an otoscope to assess how deep the infection goes and whether the eardrum is intact. They’ll likely take a swab of the discharge and examine it under a microscope to identify whether yeast, bacteria, or both are involved. This step matters because treatment differs depending on the cause.
For straightforward outer ear infections, treatment is typically a course of medicated ear drops you apply at home over one to two weeks. If allergies are the underlying trigger, addressing the allergy is essential to preventing the infection from coming back. Chronic or recurrent ear infections almost always have an underlying cause, whether that’s an allergy, a hormonal issue, or a structural problem in the ear canal, that needs to be identified and managed separately from the infection itself.