Diet can be a complicated factor in pet allergies. Most animals are not born with allergies to food; their immune systems develop an allergic response over time to some part of their diet, often one of the animal proteins. A food allergy can present in a lot of different ways, including the itching, digestive disorders, and respiratory distress already mentioned. They can be a real challenge to solve, however. You can try to figure out what’s causing your pet’s allergic reaction by feeding him different diets, but the allergic effects of food can stay in the system for eight weeks. You may have to keep your furry friend on a special hypoallergenic (non-allergy-causing) diet for eight to twelve weeks to see how he reacts, and you may have to do it several times with several different diets before you find one that doesn’t cause an allergic reaction. And while you’re feeding these test diets, you’ll have to make very sure that your pet doesn’t eat any treats, vitamins, leftovers or scraps, or even plants around the house. He has to eat the test diet exclusively for the entire eight to twelve weeks to determine whether he has an allergic reaction to it.