If symptoms are classic, and the pet responds favourably to antihistamines, a presumptive diagnosis of allergy can be made (though not a complete diagnosis). If a pet doesn't respond to antihistamines, allergic disease cannot be completely ruled out, as some dogs respond poorly, or not at all, to these medications. This often occurs in cases of food allergies and severe cases of atopic dermatitis.
Again, pets can be atopic or have a food allergy (to keep things simple). They can certainly also have both.
In cases of non-seasonal symptoms (itchy throughout the year), a food elimination trial is indicated. There are a few ways to do this. You can cook for your pet. In this case you must choose a novel source of protein and carbohydrate, i.e., something the pet has never consumed before. This could mean rabbit, horse, ostrich, kangaroo, and other things that completely gross me out. The source of carbohydrate is often either rice or potato. If you don't want the hassle of cooking the meat of these beasts, a prescription diet, made of hydrolyzed protein, can be tried for a minimum of 12 weeks. These foods include, but are not limited to, Purina HA, Medical HP, and Hill's z/d Ultra. Dogs with confirmed food allergies will respond to one of these diets in at least 75% of cases.
If the pet continues to itch after 3 months of a STRICT food-elimination trial, the dog or cat may have concurrent atopy or just atopy with no food allergy. Intradermal skin testing or serum allergy testing would be indicated in this case, with the aim to have the pet desensitized based on the results of the aforementioned tests (desensitization is essentially a process of vaccinating the patient, slowly however, with multiple and frequent injections, to slowly build up antibodies against the offending antigens).
If your dog or cat has chronic and/or recurrent skin problems, talk to your vet about allergic skin disease. Just be very patient as the diagnosis may take a while to elucidate, and the response to therapy may also require time and trials. Just keep the communication up with your vet because he/she needs to know what works, and what doesn't!
Remember, not only allergies cause itchy skin in dogs and cats.
They may be hypoallergenic.
