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Allergies in Cats

Contact Allergy
Flea Allergy
Inhalant Allergy
Food Allergy
Treatment of Inhalant Allergies Resulting In Dermatitis
Treatment of Inhalant Allergies Resulting in Respiratory Involvement
Treatment of Food Allergies
Treatment of Flea Allergies


One of the most common conditions affecting cats is allergy. In the allergic state, the cat's immune system "overreacts" to foreign substances (allergens or antigens) to which it is exposed. Those overreactions are manifested in three ways. The most common is itching of the skin, either localized (one area) or generalized (all over the cat). Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing. Sometimes, there may be an associated nasal or ocular (eye) discharge. The third manifestation involves the digestive system, resulting in vomiting or diarrhea. The latter is seen primarily with food allergy.

Types of Allergy

There are four known types of allergies in the cat: contact, flea, food, and inhalant. Each of these has some common expressions in cats, and each has some unique features.

Contact Allergy

Contact allergies are the least common of the four types of allergies. They result in a local reaction to the skin. Examples of contact allergy include reactions to flea collars or to types of bedding, such as wool. If the cat is allergic to those, there will be skin irritation and itching at the points of contact. Removal of the contact irritant solves the problem. However, identifying the allergen can require some detective work.

Flea Allergy

Flea allergy is common in cats. A normal cat experiences only minor irritation in response to flea bites, often without any itching. The flea allergic cat, on the other hand, has a severe, itch-producing reaction when the flea's saliva is deposited in the skin. Just one bite causes such intense itching that the cat may severely scratch or chew itself, leading to the removal of large amounts of hair. There will often be open sores or scabs on the skin, allowing a secondary bacterial infection to begin. The area most commonly involved is over the rump (just in front of the tail). In addition, the cat may have numerous, small scabs around the head and neck. These scabs are called miliary lesions, a term which was coined because the scabs look like millet seeds.

The most important treatment for flea allergy is to get the cat away from all fleas. Therefore, strict flea control is the backbone of successful treatment. Flea allergy cannot be ruled out just because a cat is kept indoors. Since a single flea bite can cause the reaction, it is possible, although unlikely, for a flea to get into the household and bite the cat. Therefore many times we will empirically treat a cat with a flea treatment to both prevent flea bites and kill any fleas that may be present to rule out fleas as a cause of the allergy. If a secondary bacterial infection occurs, appropriate antibiotics must be used.

Inhalant Allergy

Cats may be allergic to all of the same inhaled allergens that affect us. These include tree pollens (cedar, ash, oak, etc.), grass pollens (especially Bermuda), weed pollens (ragweed, etc.), molds, mildew, and the house dust mite. Many of these allergies occur seasonally, such as ragweed, cedar, and grass pollens. However, others are with us all the time, such as molds, mildew, and house dust mites. When humans inhale these allergens, we express the allergy as a respiratory problem; it is sometimes called "hay fever." The cat's reaction, however, may manifest as either generalized itching/licking, or respiratory system involvement.

Most cats that have an inhalant allergy are allergic to several allergens. If the number is small and they are the seasonal type, itching may last for just a few weeks at a time during one or two periods of the year. If the number of allergens is large or they are they are present year-round, the cat may itch constantly.

Food Allergy

Cats are not likely to be born with food allergies. More commonly, they develop allergies to food products they have eaten for a long time. The allergy most frequently develops in response to the protein component of the food they have been eating; for example, beef, pork, chicken, or turkey. Food allergy may produce any of the clinical signs previously discussed, including itching, digestive disorders, and respiratory distress.


Inhalant Allergies Resulting In Dermatitis

Treatment depends largely on the length of the cat's allergy season. The ideal treatment, of course, would be to eliminate the offending allergen from the cat's environment. Because this may be difficult, either because the allergens can't be easily identified, or because their elimination isn't possible (as in the case of pollens, molds, etc.), treatment to control the symptoms may need to be undertaken. It involves two approaches. One approach involves blocking the inflammatory pathway; the other involves desensitizing the cat to his or her specific allergies. We stress that, as in humans, our goal is control vs. cure.

To block the inflammatory pathway, antihistamines and/or essential fatty acid supplementation are often tried initially because they can usually be quite effective and cause the least amount of side effects. When these fail to resolve or greatly improve the allergy, steroids may be the next step. Steroids will dramatically block the allergic reaction in most cases. These may be given orally or by injection, depending on the circumstances. The side effects of steroids are much less common in cats than in people, but can occur. If steroids are appropriate for your cat, you will be instructed in their proper use.

The second major form of allergy treatment is desensitization with specific antigen injections (or "allergy shots"). This requires allergy testing/skin testing by a veterinary dermatologist. Once the specific sources of allergy are identified, very small amounts of the antigen are injected weekly. This is all in an attempt to reprogram the body's immune system. It is hoped that as time passes, the immune system will become less reactive to the problem-causing allergens. If desensitization appears to help the cat, injections will continue for several years. This approach tends to be quite effective in cats. Steroids are not used with this treatment protocol, except on an intermittent basis. This approach can not be used with food allergy.

Although desensitization is the ideal way to treat inhalant allergy, it does have some drawbacks.

  1. Cost: This is the most expensive form of treatment.
  2. Age of Patient: Because many cats develop additional allergies as they get older, young cats may need to be re-tested 1-3 years later.
  3. Success Rate: About 50% of cats will have an excellent response. About 25% get partial to good response. About 25% get little or no response. The same statistics are true for people undergoing desensitization.
  4. Food Allergies: Cannot be diagnosed with skin testing.
  5. Time of Response: The time until apparent response may be months to a year or more.
  6. Interference of steroids: Cats must not receive steroids for weeks prior to testing; these drugs will interfere with the test results.
  7. Other allergies (such as food, etc.) ideally must be ruled out first.

Inhalant Allergies Resulting in Respiratory Involvement

Although skin testing may be undertaken to try to determine offending allergens resulting in respiratory involvement, it is more commonly reserved for, and is most reliable, for allergens resulting in skin involvement.

In many cases of inhalant allergens resulting in respiratory involvement, an underlying cause cannot be identified. In this case our goal with medical management is to control the symptoms so that the cat has a good quality of life. The mainstay of therapy involves dilating the airways (which are narrowed as a result of the allergies) and reducing the airway inflammation that results in response to the inhaled allergens.

Food Allergies

We recommend testing for food allergy when the clinical signs (whether skin, gastrointestinal, or respiratory) have been present for several months, when the cat has a poor response to antihistamines and/or steroids, when the cat needs steroids on an ongoing basis in order to control symptoms, or when a very young cat itches without other apparent causes of allergy. Although there are blood tests available for food allergy (i.e. to determine which foods to which the cat may be allergic), the reliability of these tests in cats is so low that we do not recommend them. Occasionally, though unfortunately not often, changing the cat's diet from one commercial product to another may be helpful in resolving the cat's symptoms; this is not often successful, however, in cats with true food allergies since commercial diets usually contain multiple sources of protein (so determining which protein is the culprit is not possible). Testing for food allergy is best done with either a therapeutic prescription hypoallergenic diet or a veterinary nutritionist formulated home-cooked diet.

These diets are best for two reasons:
1.) They contain only one source of protein, and
2.) the protein should be one to which the cat has not ever been previously exposed, i.e. a "novel" protein. A true food trial should always meet these two criteria (and commercial foods do not). (As an aside, commercial lamb-based diets, which many owners consider to be "hypoallergenic," and which companies may label as "hypoallergenic," are not hypoallergenic diets, because they contain lamb, as well as other sources of protein. Even the prescription therapeutic lamb-based diets, which contain lamb as the only source of protein and which were initially formulated back when no commercial foods contained lamb, thus making it a "novel" protein formula for most cats cannot be used in food trials any more in those cats who have eaten lamb based diets previously. This is because, for those cats, it is no longer a novel protein.) It has become very frustrating for veterinarians, veterinary nutritionists, dermatologists, etc. with more and more pet food companies expanding their ingredient list in order to appeal to the consumer they are adding more exotic-sounding grains and protein sources, making it harder and harder to find novel protein sources for our allergic pets. This also makes it extremely difficult to obtain thorough diet histories on those cats who are having food-related medical problems. Once a food trial is begun, because it may take at least 8 weeks for all other food products to get out of the system, the cat must eat the special diet exclusively for 8-12 weeks (or more). If positive response occurs, you will be instructed on how to proceed. If the diet is not fed exclusively, it will not be a meaningful test. We cannot overemphasize this. If any types of table food, treats or vitamins are given, these must be discontinued during the testing period.

Because cats that are being tested for inhalant allergy generally itch year round, a food allergy dietary test can be performed while the inhalant test and antigen preparation are occurring.

Flea Allergies

Treatment, to be successful, must rid both the cat, as well as his or her environment of fleas.

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