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One of the most common conditions affecting cats is allergy. An allergy occurs when the cat’s immune system “overreacts” to foreign substances called allergens or antigens. Allergens and antigens are simply foreign proteins that the body’s immune system tries to remove. These overreactions are manifested in one of three ways:
There are four common 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.
“In an allergic cat, just one bite can result in intense itching that can last for days.”
In spite of common belief, a normal cat experiences only minor skin irritation in response to flea bites. Even in the presence of dozens of fleas, there will be very little itching. On the other hand, the cat with flea allergies has a severe reaction to flea bites. This occurs because the cat develops an allergic response to proteins or antigens that are present in the flea’s saliva. When a flea bites a cat, some of its saliva is injected into the skin. In an allergic cat, just one bite can result in intense itching that can last for days. Cats with flea allergy dermatitis (FAD) do not have to be infested with fleas; a single flea is enough to cause a problem!
The cat’s response to the intense itching is to chew, lick, or scratch the affected site or sites. This causes hair loss and can lead to open sores or scabs on the skin, allowing a secondary bacterial infection to develop. The area most commonly involved is over the rump, just in front of the tail. Many flea-allergic cats chew or lick the hair off their legs. Itching and hair loss around the tail base, neck and head should be considered suspicious for flea allergy dermatitis. In addition, the cat may have numerous, small scabs around the head and neck. These scabs are often referred to as miliary lesions, a term that was coined because the scabs look like millet seeds.
Since the flea saliva causes the reaction, the most important treatment for flea allergy is to prevent fleabites. Strict flea control is the foundation of successful treatment. There are many highly efficacious flea control products, both for treating the cat and for controlling fleas in the environment.
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. Food allergies are now estimated to be the second leading cause of allergic dermatitis in cats. The allergy most frequently develops in response to the protein component of the food; 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. Food allergy testing is recommended when the clinical signs have been present for several months. Testing is done by feeding an elimination diet or a special hypoallergenic diet. Because it takes at least eight weeks for all other food products to get out of the system, the cat must eat the special diet exclusively for a minimum of eight to twelve weeks. If a 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. This means absolutely no treats, other foods, people foods or flavored medications during this period. We cannot overemphasize this. Even accidentally providing a tiny amount of the offending protein can result in invalidating the test.
Inhalant allergy or atopy is estimated to be the third most common type of allergy in cats. It is sometimes referred to as “seasonal allergy” when related to pollens.
“Most cats that have an inhalant allergy are allergic to several allergens.”
Cats may be allergic to all of the same inhaled allergens that affect humans. These include tree pollens (cedar, ash, oak, etc.), grass pollens (especially Bermuda grass), weed pollens (ragweed, etc.), molds, mildew, and the common 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. Atopy is also sometimes called “hay fever”. The cat’s primary reaction to atopy is severe, generalized itching.
Most cats that have an inhalant allergy are allergic to several allergens. If the number of allergens is small and they seasonal, 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 present year-round, the cat may itch constantly.
“Some allergens may be absorbed through the skin.”
Treatment depends largely on the length of the cat’s allergy season.