Although adverse reactions to foods are not common, they may be difficult to diagnose, and frustrating to treat. Food intolerance, or non-immune mediated reactions to foods, may be caused by contaminants is the diet such as toxins, bacteria, food additives that cause idiosyncratic reactions or vasoactive amines. Food intolerance affects the gastrointestinal tract more commonly than the skin, and is treated by switching to a different diet.
Food allergies are immune-mediated reactions to normal foods.
4 food allergies have been observed in dogs and cats. Factors that influence the likelihood of an allergen reaction to a food include the number of proteins in a diet, the amount of protein, the availability of the protein to the immune system in the intestinal tract, and the immunogenicity of the protein. Food allergy is one of three major causes of pruritus in animals, the two are flea allergy dermatitis and atopy. Recognition of these three causes is important for an understanding of management of pruritus in animals, because effective therapy of any of the causes may reduce the animal's level of itching to below the clinical threshold. This is important because treatment failure or appearance of one of the other causes of pruritus may lead to return of signs.