What Causes a Dog's Ears to Discharge Pus?

Many dog owners first notice something’s wrong when they spot a yellow or brown fluid on their pup’s ear flap, or catch them scratching so hard they whimper. That discharge—often thick and smelly—is pus, and it’s almost always a sign of an underlying issue that needs attention. Ignoring it not only makes your dog miserable but can also lead to more serious problems down the line, especially if infections spread deeper into the ear canal.

Bacterial infections are one of the most common triggers for ear pus in dogs. These often start after moisture gets trapped—maybe from a swim in the backyard pool or even just a bath that didn’t get properly dried. Breeds with floppy ears, like Cocker Spaniels or Basset Hounds, are extra prone because their ears don’t get much air flow, creating the perfect warm, damp spot for bacteria to grow. Most vets will recommend a cleaning solution and antibiotics to clear this up, but skipping that visit can let the infection linger.

Ear mites are another culprit, especially in puppies or dogs that spend time at dog parks or boarding facilities. These tiny parasites burrow into the ear canal, causing intense itching and irritation—so intense your dog might shake their head until they get a hematoma. The pus from mites is usually dark brown, almost like coffee grounds, and can spread quickly if other pets in your home aren’t treated too. In places like California, some counties require reporting persistent parasite issues to local animal control to prevent outbreaks.

Allergies, too, often show up first in a dog’s ears. Food allergies (common with grains like wheat or proteins like chicken) or environmental triggers (like pollen from oak trees or grass) can make the ear lining inflamed. That inflammation cracks the skin, letting bacteria or yeast move in and create pus. If you notice your dog’s ears act up every spring or after trying a new kibble, a vet can help identify the allergen—this isn’t just for comfort, but to follow laws that require providing adequate care for chronic conditions.

It’s also important to remember that some home remedies can do more harm than good. Pouring hydrogen peroxide or olive oil into your dog’s ear might seem easy, but it can damage the eardrum or push pus deeper. In the UK, the Animal Welfare Act 2006 classifies neglecting a treatable condition as cruelty, so taking your dog to a licensed vet isn’t just a choice—it’s a legal responsibility. Even small signs of pus need a checkup to rule out serious issues like ear polyps.

Your dog can’t tell you their ear hurts—they can only scratch, shake, or pull away when you touch it. Catching pus early and getting vet care right away keeps them comfortable and keeps you on the right side of local pet laws. Regular ear cleanings with vet-recommended products can also prevent many of these issues, turning a stressful problem into a simple part of your weekly care routine.