Our dog was having infections on the skin inside his ears all the time (would come and go with treatments). The vet finally sent blood work in to test for allergies. Came back with a list 4 pages long of stuff that he is allergic to! He’s on a “meat-lovers” diet now.
A month later his ears are great without meds and he's lost down to where his weight should be.
I never feed any purchased treats. The cat food thing several years ago scared me to death. If we are traveling I buy him some made in TN human jerky for treats.