The most common causes of allergic, itchy skin in dogs are fleas, environmental triggers, and ingested proteins. Veterinary dermatologists usually begin by making sure that flea allergy dermatitis is ruled out with consistent and effective flea control. When that is accomplished, a food allergen elimination diet is often prescribed for a 6 week or longer period, followed by a re-challenge with individual proteins if there is significant improvement. This is a long process and it is tempting to take shortcuts.
Commercial tests for food sensitivity are available, but have not proven accurate in multiple studies over the years. Serum allergy tests marketed to veterinarians as well as hair and saliva tests marketed to pet owners have consistently failed to predict protein sensitivities accurately in independent studies. False positive findings are frequently reported, including when fake fur fibers from stuffed animals are submitted.