Food allergies, or food hypersensitivities, are caused by a hypersensitivity to a component (allergen) within the diet. The allergen may be a protein or carbohydrate source or may be a preservative or food additive. Signs of food allergies often occur after a cat has been on a particular food for a while. This is because it can take repeated exposure to an allergen to sensitize the immune system. Cats can develop food allergies to food components even if they have been on the same food for years.
Symptoms of Food Allergies
- Itchiness (pruritus) that is not seasonal, typically begins around age 1–3 years, but can occur at any age
- Hair loss or skin irritation (scabs or rashes) commonly around the ears, eyes, face, neck, and/or feet but can occur anywhere
- Chronic or recurrent ear infections
- Gastrointestinal problems, such as vomiting and diarrhea
Symptoms of food allergies can look very similar to those associated with environmental allergies or inflammatory bowel disease (if vomiting and diarrhea are present). Diagnostic tests are often conducted to differentiate between the types of allergies.
Testing for Food Allergies
Currently there is no reliable skin or blood test available for food allergies. Diagnosis requires an elimination trial, typically with a hypoallergenic diet. A hypoallergenic diet is either a homemade or prescription diet that contains a protein and carbohydrate source that the cat has rarely or never been exposed to (examples: venison, rabbit, and duck). The diet trial must be with this food only. The skin is monitored for signs of improvement over a period of 6 to 8 weeks. It is important to note that during the trial, your cat CANNOT have other foods or treats of any kind. If there are multiple pets, access to other foods must be restricted. Indoor/outdoor cats may need to be kept indoors to ensure dietary restriction.
In some cases, your veterinarian may elect to try hydrolyzed protein diets. These prescription diets have proteins that are broken down to lower molecular weights in order to reduce allergic stimulation. As with hypoallergenic diets, only this food should be feed for the duration of the diet trial. Just switching your cats’ food to another regular cat food may not alleviate symptoms as many cat foods contain similar ingredients. Multiple diet trials may be necessary to identify the source of allergy. If the food trial is not conducted properly, there is no way to know if the cat truly has a food hypersensitivity.
Response to diet trials may occur within a few days or a few weeks. Inflammation of the skin will decrease and itchiness will resolve. If improvement occurs, you can start to add other ingredients back into the diet to try to determine what food component is triggering the allergic response. In some cases, cats can be allergic to multiple allergens and only a partial response may be observed with a food trial. If no improvement is observed with the food trial, the skin allergy may be due to environmental allergens and not a food allergy.
Other Therapeutic Options
Depending on the severity of the allergy and response to food trials, your veterinarian may make several other therapeutic recommendations.
Fatty Acid Supplements—These products are NOT analogous to adding oil to the pet's food. Instead, these special fatty acids act as medications, disrupting the production of inflammatory chemicals within the skin. They are often used in conjunction with antihistamines.
Antihistamines—Only about 30% of cats respond to antihistamines, but side effects are less common that with steroids. You may have to try several different antihistamines to determine which works the best for your cat. Cats that do not respond completely to antihistamines alone may do well on a lower dose of steroid when used in combination with antihistamines.
Prednisolone (or other steroids)—These cortisone-type medications reduce inflammation of the skin by blocking production of inflammatory substances within the body. At the beginning of treatment, steroids may be administered at a high dose to induce a more rapid response. The dose will then be tapered down to the lowest dose possible to try to avoid potential side effects.
Potential Steroid Side Effects (associated with high doses or long-term use)
Anticipated or ‘Acceptable’ side effects
- Increased thirst
- Increased appetite
- Increased urination or larger urine volume
'Unacceptable' side effects
- Immune suppression: upper respiratory infections, urinary tract infections
- Diabetes mellitus- which may resolve after steroids are discontinued
- Congestive heart failure- if heart disease is present
Alternatives to Steroids
In some cases, a different immunosuppressive drug may be prescribed. Cyclosporine is a drug that modulates the abnormal immune reaction in allergic animals. It is used in cats when other treatments have failed or in those cats that cannot tolerate steroids. It is a relatively expensive medication compared to steroids but is not associated with as many side effects.
Unfortunately, there is no cure for food allergies. The only way to eliminate an allergy is to eliminate exposure to the food source, which may be difficult in some cases. Most treatments aim to alleviate the symptoms associated with the allergy. Coping with an itchy cat can be a very frustrating experience—we are here to help you keep your cat as comfortable as possible.
Adapted from: ‘Food Hypersensitivity’ by Catherine Outerbridge.