Merck's name for it is otitis externa, inflammation of the lining of the ear canal, and its list of signs is the list owners bring in: head shaking, a foul smell, red skin, swelling, scratching, discharge, scaly skin, an ear that is painful or itchy. One ear or both.
Merck lists parasites, an object stuck in the canal, allergies, infection with bacteria or yeast, and a middle ear infection, and adds that the shape of some dogs' ears and canals makes them more likely to get it. Then the line that explains the dog whose ears are treated every few months: unless every cause is treated, the condition often returns. The bacteria and yeast are usually the result of something else, and drops that clear them without finding that something buy a few weeks.
If the vet suspects the middle ear is involved, Merck says more tests are needed. A head tilt, loss of balance or a dog that circles is a same-day visit.
Merck describes it as finding and correcting the underlying causes and relieving the pain, with cleaning and medication into the ear. Two rules from the same page: no cotton swabs, and the treatment must continue until the infection is fully cleared, which is why the vet books a recheck rather than trusting a quiet dog.
Merck calls otitis externa the most common ear canal disorder in cats too, with parasites, foreign objects and allergies among the causes. Ear mites are treated with antiparasitic drugs. And a warning that applies to dogs as well: home remedies should be avoided, because they irritate the inflamed canal and increase the secretions that let bacteria and yeast grow.
Ear infections that keep coming back are one of the common signs of food allergy, and allergies are on Merck's list of their causes. Why does my dog keep itching? has the order vets rule out the causes of itching in, and the food trial done properly.
Write the date it started and which ear, and what came out of it in the log on My Pet. The vet sheet prints it, and "since Tuesday" beats "recently".
Read 18 September 2026.