Food allergies in cats make up to 5-10% of feline allergies.
All cat breeds can have food allergies, they are not a breed-specific thing. Still, cats with pre-existing allergies are more likely to develop food allergies than otherwise healthy cats.
Often when we think of food allergies, our first thought is that the symptoms would appear in the intestines. With cats, however, the symptoms mostly occur in the cat’s skin.
Food allergy is not something the cat is born with. It takes a long time for a cat to develop a food allergy. This kind of slowly developing allergy is called delayed hypersensitivity. The cat begins to develop antibodies to the proteins it has been eating for a long time, and this causes the allergic reactions.
So if your cat shows food allergy symptoms, they are not caused by anything new the cat has eaten recently - this form of allergy is not a quick reaction to something the cat just ate. If your cat gets an adverse reaction to something it ate for the first time, this is a question of food intolerance, not allergy. Food intolerances don’t cause skin problems in a cat. Real allergy is when the cat’s body reacts to toxic irritation with too much histamine.
The symptoms of food allergies in cats usually begin to occur when the cat is a few years old. Usually they do not start before the cat is two years old. They can occur earlier, at a few months of age, and can begin when the cat is surprisingly old, even over ten years of age. In all likelihood the occurrence of a food allergy is probably connected to the amount of exposure the cat has had to the allergen. So, logically, often the cat becomes allergic to the food it eats the most.
A cat can be allergic to quite a few ingredients in cat food. Some of the most common food allergens are beef, chicken or turkey, cereals (corn starch, soya, wheat gluten), dairy products, eggs, lamb peas, pork, pumpkin, rice, seafood, yeast… (Wheat is often used as a filler in many cat foods, and is often a cause of food allergies in cats. So if you see starch mentioned in cat food ingredients, it probably is wheat).
80 % of food allergies in cats are caused by beef, dairy and fish. If we look at these closer, then maybe 40% of food allergies are caused by fish and seafood. 10% of allergies are caused by dairy products (if you see caseinate mentioned in cat food ingredients, this tells you dairy products have been used).
Food allergy is mostly caused by proteins in cat foods (both canned meat and meat derivatives in dry food), but also the artificial colors and preservatives in cat food can cause allergies.
As mentioned above, the symptoms don’t show so much in the cat’s intestines than they do on the skin.
The most common symptom is a non-seasonal itch the cat developed at its adult age. This is a very intense itch, especially in the front part of the body: neck and head and face may itch unbearably. (In this the symptoms resemble flea allergy, so just in case do check for fleas too). There may be facial swelling. The cat may scratch, lick and chew its hair off on the itchy areas.
Skin is the body’s biggest organ, and also the main organ of defense in cats. Many of the toxins exit the body through the skin, so it is no wonder the allergy symptoms show most intensely on skin, as compared to other organs.
The skin allergies in skin often cause the cat to develop miliary dermatitis (the skin has red, crusty bumps – and not only on neck and face but flanks and belly). This is the result of excessive grooming by the cat. Also the cat may have an excessively oily skin and loose the sheen of its coat. In worst cases the cat has groomed its hair off. The skin may have a bad smell because of infection.
It is somewhat odd that many of the symptoms appear mostly on the cat’s head, and it seems that food allergies in particular cause more histamines to be released in the head area than other allergies.
Head shaking is one symptom – and may be caused by ear infections (Otitis Externa), which are common with food allergies. There can be redness and discharge from the cat’s ears. If these ear infections are recurring and resistant to treatment, it may be a case of food allergy.
Often digestive problems are more symptomatic of food intolerance rather than food allergy. But food allergy can cause diarrhea and gas in a cat.
If your cat has diarrhea, remove milk from its diet – cats are lactose intolerant so cow’s milk is not good for them if they are no longer kittens.
The cat may also vomit because of food allergies, but this symptom also is more likely to be about food intolerance.
A bad food intolerance may be connected to inflammatory bowel disease in cats.
Food allergy may also cause trouble in respiratory system of a cat.
If some or all of these symptoms have persisted for a months, and steroids don’t have an effect, check for food allergy.
You can read about diagnosing and treating food allergies in cats here.
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