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Allergies in Cats

What is an allergy?

Allergies are the result of a malfunction in the immune system. The immune system keeps infectious organisms like bacteria, fungi and viruses from infecting the body and fights any that might get in. When the immune system starts over-reacting and fighting a substance that is harmless we see an allergic reaction.

Allergies are not restricted to humans. It is a common source of discomfort for dogs and cats. Often the appearance of scabs and sores on an otherwise healthy cat is an indication of an allergic reaction.

What causes allergies in cats?

As in humans, an allergic reaction is caused when a cat comes in contact with a substance to which it has developed a sensitivity.

The 4 most common causes of allergies in cats are:

Allergies to flea and other insects

This kind of allergy is the most likely cause of a cat allergic reaction. Fleas inject saliva in the cat when it bites and there are many substances present that can trigger a reaction. Like humans, it is possible to trigger a reaction with a very small amount of irritant. Sometimes only one flea bite is all it takes.

Symptoms of Flea induced allergic reactions.

The usual symptoms include scabs, thin unthrifty fur in the area and bumps. The cat will want to scratch and bite the irritated area making the reaction worse. It may also lick or groom excessively. Areas most affected is usually at the base of the tail and the area around the lower back. The head and around the ears can also be affected. Sometimes the sores get infected.

Flea Allergy Dermatitis (or FAD) is the name of the condition. The sores and scabs are sometimes referred to as Miliary dermatitis. This is a descriptive term used in veterinary medicine to describe a multifocal distribution of skin lesions, with no identifiable pattern. The term miliary means millet-like, as the feel of running one's hands through the coat of an affected cat is comparable to the feeling if a cat's coat contains millet seeds. (from Wikipedia) Fleas are the most common cause of allergic reactions, mosquito bites, ticks, and other insects can also cause reactions.

Prescription between the shoulder-blade drops is one of the safest ways of controlling fleas in cats. Like all insecticides it should be used as per instructions, but it has a good history of safety. Advantage II Flea prevention Large Cats, over 9 lbs, 6 doses (Packaging May Vary). Some cats are more sensitive than others so keep an eye out when you first apply it in case your cat reacts to it. I've used it for years and only had one cat who once had a reaction and he only reacted once.

How is a flea allergy diagnosed?

The irritation is fairly characteristics and recognizable. Diagnosis is often confirmed by treating the animal for fleas and seeing if there is an improvement. Along with flea treatment of the cat its living area must also be rid of fleas.

If flea treatment is ineffective then biopsy or scraping of the affected area might be performed. Further investigation might include subdermal injection of selected irritants and observation of reactions. This is similar to human diagnostic techniques.

If the cause is mosquito or other biting fly, removal from exposure will be a good indication of the cause.

Cat Flea Life Cycle and Control page


Besides treating the cat and its living quarters to get rid of fleas any side conditions will be treated. If infection has developed in the affected area, then antibiotics might be prescribed.

Antihistamines or steroids might be used to deal with irritation and reduce itching.

Hyposensitisation therapy might be used. As in human "allergy desensitization--allergy shots" a cat might be injected with gradually increasing doses of flea antigens. This treatment gradually desensitises the immune system and reduces the allergic reaction.

Food allergies

Food allergy in cats is not uncommon. This might be triggered by grains in particular wheat, dairy products, eggs, or animal proteins such as fish and beef.

Symptoms of food allergies

Typical symptoms involve signs of digestive problems, such as diarrhea and gas. It is not unusual to see irritation around the head, ears, neck and face. This irritation causes itching and scratching. There might be swelling and infections might occur. This occurs also in the ears. The hair might be thin in affected area because the cat scratches or licks excessively. Unlike insect allergies the food allergy is not seasonal and will occur all year round.

Diagnosis of food allergies can be tricky.

Exactly as in human allergic reactions to food, identifying the culpit can be difficult. As in humans, a restricted diet is prescribed. No supplements or treats are allowed. By adding or substracting elements of the diet the offending food can be identified and eliminated.

Cats can develop allergies to new foods that were not offensive before, as they can gradually adjust to previously irritating foods.

Treatment of a food allergy

Treatment is usually easy once you've identified what causes the problem, just avoid it. People have sometimes found that home made diets is successful where commercial food causes difficulty. The problem then becomes one of providing a balanced diet.

Direct contact sometimes causes Allergies.

Cats have sensitive skins and will be irritated by strong soaps or shampoos or flea medication not intended for cats. They will also be irritated by acids or strong bases. These are not strictly allergies. They are irritation caused by strong chemicals. The term used for this is Irritant Contact Dermatitis, or simply Contact Dermatitis.

On the other hand some substances will trigger an allergic reaction and this is referred to a Allergic Contact Dermatitis.

Symptoms of Contact Allergy

Non seasonal itching (it might be seasonal if the material causing the irritation is a plant) in spots that don't have much fur. There is sometimes blisters, bumps or pimple like sores, rashes or redness. Often the reaction goes away after the irritant is no longer in contact with the cat. Think poison ivy in humans.

skin might be red, inflamed or thickend.

Diagnostic of Contact Allergy

Diagnostic can be tricky. First step will be eliminating the possibility of flea allergy and the possibility that the irritation is caused by a chemical non allergy reaction.

Your vet will want to talk to you and determine what materials your cat has been in contact with. He might apply various substances to your cat's skin and observe the reaction. This is a common test for humans. The patch test is positive if there is irritation, redness or if the area shows swelling or blisters.

A biopsy of the skin might be done.

Removing a cat from an area or preventing it from going out might bring relief and give indication of what is causing the allergic reaction.

Treatment of Contact Allergic Reaction

Treatment will principally consist of removing the irritant or removing the cat from the area where the irritant is found, and dealing with the irritation. If there is a secondary infection this will be treated with antibiotics. The vet might prescribe corticosteroids to help stop itching and scratching.

Allergies due to inhalation of irritating substances

Like humans cats can be allergic to pollen, dust mites, mould and dust. It is a difficult allergy to diagnose.

Symptoms of inhalant or atropy Allergy

Miliary dermatitis (see above) accompanied of itching and scratching. Presents mostly around the head and back but can also be in the ears. Hair thinning or loss may be present. Face might be scabby.

It is one of the causes of Feline eosinophilic granuloma complex. This is considered to be a cutaneous (skin) reaction pattern that can be the manifestation of a number of underlying infections, in particular allergies or ectoparasite infestations. (Wikipedia).

Diagnostic of Inhalation allergy

It is tricky to diagnose this form of allergy. As in other form of allergies, this can look like other things and a vet will need to gradually eliminate other causes. He might do a biopsy or skin scraping to help eliminate mange or other infections. Blood test to identify antigens might be done. In cats, an enzyme linked immunosorbent assay also known as ELIZA and Radioallergosorbent test known as RAST are sometimes done. As in contact allergy, a patch test might be run.

(ELISA), also known as an enzyme immunoassay (EIA), is a biochemical technique used to detect the presence of an antibody or an antigen in a sample. In simple terms, in ELISA, an unknown amount of antigen is affixed to a surface, and then a specific antibody is applied over the surface so that it can bind to the antigen. This antibody is linked to an enzyme, and in the final step a substance is added that the enzyme can convert to some detectable signal, most commonly a colour change.

The RAST test is an alternative to skin tests to identify allergens. Advantages of the RAST test range from: excellent reproducibility across the full measuring range of the calibration curve, it has very high specificity as it binds to allergen specific IgE, and is extremely sensitive too, when compared with skin prick testing. In general, this method has a major advantage: it is not always necessary to remove the patient from an anthihistamine medication regimen, and it can be done even if the skin conditions (such as eczema) are so widespread that allergy skin testing cannot be done.

Treatment of Inhalant Allergies

As in other allergies any infection is treated with antibiotics or fungal remedy. The cat might be given allergy shots to desensitize him. Corticosteroids are effective and cause relief of symptoms such as scratching and irritation, but do not cure allergies.

There is some evidence that supplements of Essential Fatty Acid sometimes work.

It is difficult to eliminate air borne substances, and humans have had to deal with hay feaver and similar ailments for ages.

Cats can also suffer from allergies to vaccines and medication.

This kind of allergy is usually easier to identify and prevent since there is a clearer cause and effect. Cats do not take medicine and vaccines on their own.

Many people are allergic TO cats.

There is a great deal of research going on in this field right now. Recently scientists have identified how allergic reaction to cats are triggered. The link is to the BBC news page. Elsewhere a vaccine is being developed by McMaster University researchers. The link is to a Globe and Mail article.

emails: Christine

This article is provided for information only. It is not to be used instead of consulting a VET. If your kitty is sick get some help.