The bottom line first: sour-smelling ears, more black or yellow discharge, and repeated head shaking usually point to an ear infection. Because the right medication depends on whether bacteria, yeast or mites are behind it, don't guess at home โ have a vet check the discharge.
Otitis externa is inflammation of the ear canal lining โ the passage running from the ear opening down to the eardrum. Your dog can't tell you it hurts, so it comes out as behavior instead.
Left untreated for a long time, the skin lining the canal thickens and the canal itself narrows, which makes medication harder to get where it needs to go. Severe chronic cases can end up needing surgery, so a little scratching is not something to keep waiting out.
A dog's ear canal isn't straight like ours โ it runs down vertically and then turns horizontally, in an "L" shape. That shape protects the deeper ear, but it also means water and wax that get in don't drain out easily. Add a humid rainy season and the canal stays warm and damp, which is exactly the environment bacteria and yeast multiply in. That's why infections so often show up after a bath, a swim, or a walk in the rain.
Some dogs are working against their own anatomy. Breeds with large, floppy or hairy ears โ cocker spaniels, poodles, Old English sheepdogs and similar โ get less airflow through the canal and are more prone to infection. For these dogs it's worth lifting the ear and checking often through the summer.
The most frustrating thing about ear infections is that they improve on medication and then return once it stops. That usually isn't a care failure โ it's because the ear infection is the result of another problem. Allergies are the most common driver: veterinary sources report allergies are involved in as many as 43% of ear infection cases, and that 65% to 80% of dogs with food allergies develop ear infections. Hormonal disease such as hypothyroidism, foreign material like grass seeds, ear mites (especially in puppies), and stopping medication early because things look better are other frequent reasons.
So for a dog with recurring infections, treating only the ear isn't enough. Noting the skin-related signs alongside it โ paw licking, redness on the belly or armpits, more eye discharge โ and bringing that to your vet makes the underlying cause much easier to find. If you're reviewing diet, start by tightening up treats and table food, and check Foods Dogs & Cats Can't Eat for what shouldn't be on the menu in the first place.
At the clinic, the ear is examined with a magnifying otoscope and the discharge is looked at under a microscope. That's because bacteria, yeast and mites need completely different medications, and stubborn chronic cases may even need culture and sensitivity testing. Picking a medication yourself tends to muddy the diagnosis more than it helps.
Senior dogs recover more slowly from the same problem and are more likely to have other conditions layered on top, so having them seen early is safer. If you want to know what life stage your dog is at, try the Dog Age Calculator. And while you're on summer ear care, it's worth covering the other seasonal risks too โ heatstroke and hot-pavement burns.
The medication that works depends entirely on what is causing the infection โ bacteria, yeast, or ear mites all need different treatment, so guessing without a microscopic look at the discharge can make things worse. Some cleaners are also unsafe if the eardrum is damaged, which is another reason a veterinarian needs to look inside the canal first. Avoid irritating home remedies such as vinegar or alcohol, and never push a cotton swab deep into the ear. What you can do at home is use the cleaner and medication your vet prescribed, exactly as directed and for the full course, and keep the ears dry after baths and swimming.
Ear infections are often a symptom of something else, so if the underlying cause is not addressed the infection returns as soon as the medication stops. Allergies are the most common driver: veterinary sources report that allergies are involved in as many as 43% of ear infection cases, and that 65% to 80% of dogs with food allergies develop ear infections. Hormonal conditions such as hypothyroidism, the shape and hairiness of the ear canal, foreign material like grass seeds, and stopping medication early once symptoms improve are other common reasons. If it keeps recurring, ask your vet to look beyond the ear at skin, allergy and endocrine causes.
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This content is general information and does not replace veterinary diagnosis. See a veterinarian for an accurate diagnosis, and seek care immediately if your dog is in significant ear pain, holds their head tilted to one side, or loses balance.