While there is much talk of food sensitivities, true allergies to food in pets are rare.
Food allergy has an immune basis, whereas an intolerance, for example, to a certain ingredient, like lactose (found in milk) does not.
Food allergy usually manifests itself in two ways: through tummy-associated signs and through skin problems. You can read more about tummy problems in our gastrointestinal information. More information on food-associated dermatitis can be found here.