A food allergy will result in an immune response to a particular ingredient in the diet. This can be any food product but in most cases it is usually in response to a protein in the product. Once the ingredient that causes the reaction has been identified it will need to be excluded from your dog’s diet for life.
A food intolerance is where the reaction to a particular ingredient does not cause an allergic reaction but where an ingredient can not be tolerated. In some cases, dogs may be able to eat the particular ingredient in small quantities, however, as there is no way of knowing at what level a reaction will be triggered, it is prudent to avoid the ingredient once identified.