Skin disease due to a dietary component can occur due to a immunological reaction involving type 1 hypersensitivity response or due to an non-immunological reaction. They can occur at any age from puppies and kittens to old age.
Diagnosis of intolerance to food is often challenging and involves dedication. Serum allergy testing has limitations as not all reactions are antibody mediated and often normal individuals show serum IgE and IgG antibodies to various dietary proteins.
Ultimately the diagnosis should be based on response to a strictly conducted diet trial and subsequently challenging with the original diet.
The clinical signs or atopic dermatitis and adverse food reactions can be very similar and some dogs may have both conditions. Therefore in order to get maximum response a food trial should be performed in all allergic dogs and cats