Allergies in dogs and cats can have signs and symptoms that sometimes look common or that might be attributed to something else. Pet itching and scratching are high on the list, with odor, ear infections, skin infections, surface bumps, and scooting to name a few.
Dogs and cats with allergies are itchy. They itch because histamine is released when their immune system attacks the offending allergen. Areas of the skin that most often itch are ears, eyes, feet—even between the toes—arm pits, groin, and around the anus. This itching causes feet biting, head shaking, face rubbing, and bottom scooting. Some pets also bite or scratch their bellies. About 60% of cats that pull out their hair (barbering) and have bald spots (alopecia) have itchy skin from food allergies.
Because allergic pets scratch, they damage their skin (dermatitis). Yeast grows rapidly on damaged skin, causing more itching (Malassezia dermatitis). Yeasty infections are stinky, and that's why many allergic pets have stinky, itching skin infections. Similar events cause ear infections: Ears itch, your pet scratches, yeast multiplies, and the ears itch even more. Eventually bacteria multiply within the ear.
Ear infections in pets (otitis externa) may be more common than skin infections because the ear is often the first part of an allergic pet's body to develop itching. Half of dogs with allergies have ear infections as their only obvious problem. Over time, these infections can progress to chronic ear inflammation and deafness.
Some allergic pets itch more than ever when they come home from the groomer. This occurs if the groomer uses heavily scented soaps and conditioners. Some groomers clip the hair so short, especially along the bottom, that the clippers further irritate already itchy skin. If your pet has allergies, he or she may come home from the groomer and rub him or herself on the floor, carpet, and sofa.
If your cat or dog is scratching frequently, bacteria can enter breaks in the skin and begin multiplying. Some of these bacteria, such as Staphylococcus, Streptococcus and Pseudomonas, cause serious infections so that your pet needs antibiotics to recover. Antibiotics clear the skin infection but do not remove the underlying problem, which is allergies. Without addressing the tendency to be allergic, cycles of reoccurring skin and ear infections are likely.
Many pets with allergies slide on their bottoms (scooting) because the rectal area itches. Scooting looks funny but aggravates the two anal sacs located on either side of the rectum and anal sac abscess occurs.
Pets with food allergies may burp and vomit, pass gas, have diarrhea, and lose weight. Some do not have diarrhea, but have frequent stools. Food allergies are the third most common cause of skin disease after flea allergies and atopy.
Proteins cause most food allergies. It's unusual for pets to be allergic to carbohydrates or fats. Considering all dog food allergies, two-thirds are caused by beef, dairy, and wheat. Dogs are also frequently allergic to soy, chicken, eggs, and corn. For cats, 90% of food allergies are caused by beef, dairy, and fish. Cats are also commonly allergic to lamb, wheat, chicken, and corn.
For dogs and cats, the most common sign of food allergy is itching and scratching. Other signs of food allergies are head and neck itching, miliary dermatitis, eosinophilic granulomas, swollen lymph nodes, hives, and conjunctivitis.
Laboratory tests can help make the diagnosis of allergies. Some allergy tests look at the serum, the part of the blood that has WBCs and fluid, but no red blood cells. If the serum shows high levels of IgE (immunoglobulin E), it suggests your pet has allergies or has a parasitic infection that is causing an allergy-like response.
RAST (radioallergosorbent serum test) identifies your pet's reaction to specific antigens, such as food mites, fleas, and pollens. Unfortunately, interpreting the RAST test is difficult because there is no direct correlation between what your pet's blood reacts to and the degree to which your pet exhibits symptoms. This is because allergies are caused by a complex interaction of many factors, not just the antibodies your pet makes that can be measured in a test. The cost for a RAST test ranges from $200 to $500, depending upon how many antigens are tested.
Another clinical test for allergies is the intradermal skin test. Like the RAST, intradermal skin tests are expensive and somewhat difficult to interpret. With skin testing, small amounts of the material your pet may be allergic to are injected into a shaved area of the skin. If your pet reacts with increased blood flow and histamine release, there will be a wheal of red, raised, puffy skin around the injection site. As with the RAST test, there is no clear correlation between skin test results and your pet's reaction to the material in everyday life. These tests are used as indicators of what your pet should avoid, but not as definitive diagnoses.
For many pets, one of the best methods of diagnosing allergy is with a food elimination trial. Food elimination trials require pets to eat only special diets, such as the Hill's Z/D diet with all the components broken into such small segments they no longer arouse the immune system. After 3-8 weeks on Hill's Z/D, your pet receives one food with kibble for 3-8 weeks. If no symptoms occur, you know your pet tolerates this food. More foods are added one at a time. The difficulty with food elimination trials is that pets can have nothing else—no treats, bones, chewies, or flavored medications—during the test period.
Others try a home-cooked food elimination trial. With this food elimination trial, your pet eats a protein and a carbohydrate it has not been exposed to before, such as pork and peas or deer and sweet potatoes. For 3-8 weeks your pet eats nothing other than these two ingredients. No supplements, no flavored medications. After this period, one food, such as carrots, is added. Your pet continues on this diet of three ingredients for another 3-8 weeks. If your pet remains symptom-free, another food is added, gradually increasing the list of foods your pet can tolerate. Again, the difficulty with home-cooked food elimination trial is that your pet can have nothing else—no treats, bones, chewies, or flavored medications—during the test period.
If your pet has food allergies, we recommend feeding pet food specifically formulated for pets with allergies. Go! Sensitivity + Shine Salmon Recipe is one brand of pet food helpful for pets with allergies and sensitive stomachs. It is highly digestible and contains Omega 3 and Omega 6 fatty acids. Wysong Anergen Dog & Cat Dry Food is another good choice for allergic pets, as it is made with non-allergenic, high quality protein sources.