Source: Wikimedia CommonsCats often develop “food intolerances” or “food allergies” to ingredients found in commercial cat food. Currently, the most common allergies in cats are: chicken, dairy, fish, beef, lamb, and eggs.

However, an allergy can develop to any protein to which the cat is repeatedly or constantly exposed.

The symptoms of food allergy are typically skin-related and/or digestion-related.

  • Skin symptoms include rashes (particularly around the face and ears), excessive licking (typically paws, legs or tummy), and red, itchy ears.
  • Digestive symptoms include vomiting and diarrhea. These are similar to the symptoms of food intolerance (reaction to food ingredients that do not involve the immune system) and inflammatory bowel disease.

Food allergies are often confused with atopy (inhalant allergies). Both can cause very similar skin symptoms. Here’s a quick 2-minute video explanation:


There are several purported routes to diagnose allergies in humans and animals. There are blood and saliva tests, which experts say are completely worthless and inaccurate; another involves anesthetizing the animal, injecting small amounts of dozens of allergens into the skin, and noting reactions. Unfortunately, that is unreliable in cats (and not terrific in dogs, either). Truthfully, the diagnosis has to be “backed into” through trial and error, based on response to treatment. For example, if changing foods resolves the problem, then it was likely a food intolerance. If steroids give relief, then an allergy is almost certainly involved.


Steroids. One conventional treatment for food allergies is administration of steroids (also called “corticosteroids” and “glucocorticoids” to distinguish them from the anabolic steroids that bodybuilders and athletes sometimes use).

Steroids can be given by long-lasting injection (“Depo-Medrol” or other injectable cortisone) or by mouth in the form of a tablet. The two most common oral steroids are prednisone and prednisolone. Prednisone is hard for cats to metabolize and must be converted to prednisolone in the liver before it will work. Therefore, it is simpler and less stressful to give prednisolone itself.

However, steroids have many dangerous side effects. The injectable forms in particular can cause diabetes. Steroids can also damage the kidneys over time. The primary action of steroids is to suppress the immune system, so that the inflammatory reaction to the allergen does not occur. This makes the cat more prone to infections. Steroids can also cause ulcers in the stomach and intestines (especially in dogs). Cats receiving steroids should not be vaccinated because the steroid prevents the immune system from responding to the vaccine.

A short trial of steroids may be helpful in determining whether the symptoms are due to an allergy, or to some other cause, such as parasites

Hyposensitization. This therapy is not often used in cats, because it requires knowing precisely what the cat is allergic to; and this is difficult to determine with accuracy. If one or more allergens are known, then purified substances are diluted and injected to signal the immune system that the substance is not harmful, so it doesn’t need to over-react. Injections need to be given every 1 to 3 weeks.

A new approach that avoids the hassle of frequent injections is sublingual (under the tongue) therapy. It’s much easier to give to pets, and results often occur within 30 days, rather than the months it takes for injection therapy. There is also far less risk of anaphylaxis (allergic shock) and other adverse effects.

Interestingly, this therapy is strikingly similar to homeopathy in its use of very diluted substances.

Hypoallergenic Diet Trial. Diet trials use “novel” ingredients that are not commonly found in pet food. Novel protein sources include kangaroo, emu, venison, rabbit, and duck. Novel carbohydrate sources include green peas, potatoes, and barley. Lamb and rice used to be novel, but since the introduction of lamb and rice foods years ago, many animals have (predictably) become allergic to those, too. The diet ideally should contain one protein source, one carb source, vitamins, and minerals; nothing else.

The prescription-type diets (using green peas and novel meat sources) are available from some veterinarians, and there are a few OTC choices as well. However, with OTC diets, even if it looks clean, several studies have documented unlabeled, potentially allergenic proteins in a large percentage of them.

A diet trial lasts 12 weeks, in which the cat is fed only the test food; no treats, no flavored medicines, toothpaste, or supplements — no exceptions. Just one diet slip-up (such as giving a treat containing an allergen) could invalidate the entire trial and you will have to start over.

Home-cooked elimination diets are also an option. In general, a well-nourished animal will not develop any serious deficiencies in three months, even if the diet is not supplemented. But, it is probably a good idea to at least add calcium (as long as the source is pure; no egg shells, bone meal or oyster shells). Many supplements (and some medications) contain gelatin or other ingredients that could ruin the trial. Work with your veterinarian on this. Pharmacists are also excellent resources for details on drug ingredients; it turns out that many products contain wheat and/or corn.

Alternative Therapies. Holistic treatments for food allergies include homeopathy, homemade diets using novel ingredients, natural anti-inflammatories like slippery elm and antioxidants, skin-healing supplements like Omega-3 fatty acids, and other immune-supporting treatments like BioSuperfood.

It should also be noted that even in cats who are not specifically allergic to something in the food still often do better with a hypoallergenic diet. It seems that the fewer allergens the immune system has to deal with overall, the less chance it will over-react to any of them.

Click here to read Floppy Cat’s interview with Dr. Jean about food allergies.