Mountain Animal Hospital

Food Allergy in Dogs and Cats

What are the signs?

The most common sign of food allergy in dogs and cats is itchy skin.  Although food allergy can cause your pet to scratch anywhere on his or her body, the common locations are the ears, feet, and hind end of dogs and around the face and neck in cats.  Recurring ear infections in dogs is another very common sign of a food allergy.

**Did you know?? 25% of dogs with food allergy present with ONLY recurring ear infections!!**

Some dogs and cats with food allergy can also have gastrointestinal signs such as vomiting, diarrhea, and flatulence.  Most pets will develop an allergy to the protein source in the diet (such as chicken or beef), but allergies to carbohydrate sources are also possible.  It is also important to remember that food allergy takes time to develop.  Most animals that develop food allergies have been eating the offending diet for years with no trouble.

When might we be suspicious of a food allergy?

–          There has been no response to treatment for fleas and sarcoptic mange

–          Your pet’s itching is not a seasonal problem (i.e. – it is constant all year long)

–          Your pet’s itching has responded only partially to cortisone-based medications

–          Your pet develops recurring infections of the skin or ears (bacterial or yeast)

How is a food allergy diagnosed?

The ONLY way to definitely diagnose a food allergy is to perform what is called a DIET TRIAL at home.  This involves feeding a special, hypoallergenic diet for 8-12 weeks, and waiting to see if your pet’s skin and/or gastrointestinal signs improve.  Intradermal (skin) allergy testing and serum (blood) allergy testing have NOT been shown to be accurate in diagnosing a food allergy.  It’s important to remember a food trial is a diagnostic test that you are performing at home!  If your pet gets any flavored treats or other foods over the 8-12 week period, this could interfere with the results of the test!  If your pet responds well to the new diet, then after the 12 week trial we can do what’s called a “challenge study”.  This means feeding the old diet or a protein we suspect is causing the problem at each meal for 2 weeks.  If your pet gets itchy again, we know he or she is allergic to that diet or protein.  Some people prefer not to do a challenge study if their pet is doing better and choose to simply continue feeding the hypoallergenic diet.

What types of hypoallergenic diets are available?

There are two different types of hypoallergenic diets that we can use for diagnosing a food allergy.  These are called hydrolyzed protein diets and novel protein diets.  A novel protein means a protein that your pet has never been exposed to before.  Some examples of less common protein sources include duck, venison, and even kangaroo!  When selecting a novel protein diet it’s important to think back and review all of the diets that your pet has eaten in the past, to make sure we choose a “new” protein. Hydrolyzed protein diets use a conventional protein like chicken, but break the protein down into pieces that are too small to cause an immune reaction.


The following table summarizes the pros and cons of hydrolyzed and novel protein diets:

Novel protein diets Pros-          Tend to be “tastier”-          Less expensive 


–          Many less common proteins are now    available on the general market (more chance your pet may already have been exposed)


Hydrolyzed protein diets Pros-          Don’t need to be as concerned about which  protein your pet as been previously exposed toCons

–          More expensive

–          We are making the assumption that every piece of protein has been effectively cut in the processing

–          May be less “tasty”



Why not diets from the Pet Store?

Over the past several years, less common proteins like duck and lamb have now become available in the general market.  The companies who produce veterinary prescription diets understand the importance of thoroughly cleaning their facility between manufacturing a hypoallergenic diet and a non-hypoallergenic diet.  This ensures that the hypoallergenic diets are not contaminated with proteins that an allergic pet may react too.  All pet food companies, however, may not be quite so diligent and studies have found trace amounts of non-novel protein in “hypoallergenic” diets from grocery or pet stores.  A diet trail takes a lot of time, patience and commitment.  It can be frustrating when we don’t know if it’s not working because the diet has been contaminated with other proteins or if your pet actually does not have a food allergy.  This is why we recommend using a veterinary prescription diet or a homemade diet for a diet trial.