Allergies are common, but complex. Determining if your pet has an allergy, and to what, requires a thorough history, clinical exam and multiple tests. - Flea Allergy Dermatitis (FAD) results from an allergy to a protein in flea saliva, which comes into contact with the pet when the flea bites. Dogs and cats with FAD may not have a large flea burden – even a few fleas can cause itching in these animals. In dogs, red, irritated skin and hair loss over the rump, tail base and th