Hello, The true underlying cause for the repeated ear problems is an allergy. Most ear problems do involve a food allergy but that is not the only thing that can affect the ears. Contact allergies like grass, pollen, dust and molds can all irritate the skin and open the door for yeast to overgrow. In order to prevent or reduce the severity of these are flare ups I recommend year round treatment for the ears. This means cleaning the ears 2-3 times a week with a special ear cleaner like Tris-EDTA or some other medicated ear cleaner recommended by your vet. Also, you may want to put ear medication into the ears once weekly when the ears are quiet and not showing irritation.
Dogs have ear canals that are 3-4 inches long before you get to the ear drum. Even in your dog the ear drum is still 3 inches away from the top of the canal. Sometimes owners are to tentative and do not get the medication in deep enough or do not clean the ears frequently enough to get all the way down the canal where cleaners and medications can be effective. I see a lot of times that dogs with repetative ear problems are actually ear problems that never fully went away. The irritation remained deep in the canals close to the ear drum only to blossom once again up the ear canal and start the process all over again. It is because of the length of the canals and the difficulty to completely clear them of any irritation or infection that constant attention must be paid to their maintenance