The first is hypersensitivity which is a true allergic reaction to some component of the food. Most animals suffering from food allergies have skin irritation as the primary sign with only 15-20% of these showing vomiting or diarrhoea.

Hypersensitivity can be difficult to diagnose and is often identified by response to treatment with elimination diets. These are low allergy (hypoallergenic) diets which use a single protein and carbohydrate such as chicken as rice. The diet is maintained for 10 days before any changes are considered. If it has been successful other components can be gradually introduced. Where there is no improvement the protein and/or carbohydrate should be changed.

Unlike many other allergies food allergies seem poorly responsive to corticosteroid therapy

The second syndrome is food intolerance. This is not a true allergic reaction but rather an abnormal response to chemical component of a food or a toxin induced reaction such as may be seen with garbage eating. One common human food intolerance is to lactose (milk products) however the importance of this condition on dogs and cats has not been determined. This condition is not associated with skin allergies but also tends to respond to dietary management.