Common culprit

I have a two-year-old Soft Coated Wheaten Terrier who scratches a lot and her skin is a bit flaky. She just looks so uncomfortable, poor thing. My vet has confirmed she doesn’t have mange and has suggested it might be an allergy to an ingredient in her food, so I have changed brands but this hasn’t had much affect.

A friend at training suggested I try an elimination diet to see what the cause might be. Could you tell me if you think this will help, and if so, what are the common culprits as I think I should begin with one of those?

Ms Sanders, by email