Environmental causes worth ruling out alongside food
Itchy skin has plenty of non-food causes — fleas, pollen, grass, contact irritants and seasonal environmental allergens are all common culprits, and they can look identical to a food reaction from the outside.
A vet can usually help separate the two through a combination of history, timing (does it track with seasons or with specific meals?) and, where needed, targeted testing. Tackling a food elimination diet while an environmental cause goes unaddressed is a common reason these plans stall.
Timing is one of the more useful clues you can bring to a vet appointment: itching that's worse in spring and summer points toward pollen or grass; itching that's constant year-round, regardless of season, points more toward a food or dust-mite related cause.