Josephine Wills qualified from the RVC in 1981. She spent several years in practice before joining Bristol Veterinary School where she worked on chlamydial infections in cats and respiratory tract disease. In 1986 she was awarded her PhD, following this with several years post-doctoral research at the University of Manchester Medical School looking at vaccine development for chlamydial infections and epidemiology of chlamydial infection in queens and kittens. In 1988 she joined the Waltham Centre for Pet Nutrition as Veterinary Adviser and is now Veterinary Affairs Manager. AN adverse reaction to food is any clinically abnormal response attributed to the ingestion of a substance in the diet, and it does not presuppose an aetiology. True food allergy or hypersensitivity is an immunologically-mediated phenomenon; it can be antibody mediated, immune complex mediated or cell mediated. To confirm a diagnosis of food hypersensitivity, the antigen should be identified, a relationship between antigen exposure and reaction should be demonstrated, and the immunological mechanism elucidated. If these criteria have not been fulfilled, then strictly speaking the term food hypersensitivity should not be used, and food intolerance, food idiosyncrasy or food sensitivity used instead. However, in veterinary medicine it has been customary to use 'food allergy' or 'hypersensitivity' for any abnormal reaction to food, regardless of the aetiology. Allergic reactions to ingested food allergens in certain previously-sensitised cats can produce signs involving the skin, alimentary tract, respiratory tract and CNS.