Diagnosis
The symptoms of flea allergy can mimic other disorders of the skin.  Before concluding that a cat is allergic to fleas, the examining veterinarian first will have to rule out allergies to food and inhalants, internal parasites, drug reactions, hair follicle inflammation or folliculitis, fungal infection, and other topical parasites -- all of which have similar signs as an allergic reaction to fleas.  A thorough history and physical exam will be required, during which the veterinarian will analyze the type and size of the skin lesions.  Follow-up examination allows assessment of the cat's response to therapies for flea allergy.  Skin tests and allergy testing by intradermal injection may be advised.  It is possible for a cat to have coexisting allergies, making management of the symptoms more difficult.