Allergies are one of the most common health conditions in the world. Everybody knows someone who suffers mightily during allergy season, when certain molds and pollens prevail more in the environment. Unfortunately, our feline companions experience the same kinds of allergies that we humans experience, causing them the same kind of misery.

How allergies happen

Allergies occur when the immune system overreacts to substances called allergens, foreign proteins that the immune system tries to attack and remove. Allergens themselves are fairly harmless; it’s the aggressive immune response that causes the problem.

Allergens enter the body in a variety of ways:

• Inhalation (dust, mold, pollen)
• Indigestion (food)
• Through the skin (insect bites)

Allergic cats will show different symptoms, depending on the route that the allergen enters the body:

Respiratory: sneezing, runny nose, eye discharge (upper respiratory) or coughing and wheezing (lower
respiratory).

Dermatologic: itchy skin, possibly with scabs and/or hair loss.

Gastrointestinal: nausea, vomiting and/or diarrhea.

Cough and sneeze

When airborne allergens irritate the respiratory system in humans, they commonly cause sneezing; itchy, red eyes; and a runny nose. Although these upper respiratory signs are sometimes seen in cats, it’s more common for airborne allergens to cause a response in the lower respiratory tract (the lungs).

In this situation, the cat inhales the allergen, which triggers a hypersensitivity reaction. The airways constrict, and glands in the airways secrete mucus to trap the allergen and prevent it from migrating further into the lungs. The cough reflex also initiates to expel the trapped allergen. Cats who respond to inhaled allergens in this way are said to have allergic bronchitis. A more familiar term for this condition is asthma.

Do a dietary elimination trial, in which your cat is fed a diet containing a protein source she hasn’t encountered before (like duck, rabbit or venison), to obtain a definitive diagnosis.

Scratch, chew, lick

Although airborne allergens can trigger respiratory signs in cats, it’s more common for these allergens to affect the skin. When this occurs, we call the condition atopic dermatitis or atopy.

Common airborne allergens include house dust, pollens, molds, grasses and mildew. Cats with atopy are often very itchy, and they manifest this by scratching their skin and grooming excessively, which often results in hair loss.  Some cats will develop small scabs all over their body, a condition called miliary dermatitis (because the small, crusty scabs resemble millet seeds). Cats with atopy may show signs only during certain seasons, when the particular allergen is prevalent, although signs can be seen year-round as well, if the allergen is constantly present in the environment (house dust, for example).

Contact dermatitis is a fairly uncommon skin disorder in which the skin reacts to an external substance that it comes into contact with. Sometimes the skin becomes inflamed because the substance itself is irritating or caustic, like household cleaners. This irritant contact dermatitis should be distinguished from allergic contact → dermatitis in which the skin becomes inflamed because the cat is allergic to the substance that is contacting the skin, such as flea collars, certain plants, synthetic carpet material, bedding (especially wool) and some shampoos.  Allergic contact dermatitis is fairly rare in cats; I’ve only seen two or three cases at my cat hospital over the past few decades.

Flea allergy dermatitis (FAD) is the most common allergy in cats. When fleas bite a cat, they deposit their saliva into the skin before they draw their blood meal. (How’s that for a disgusting thought?) Some cats are allergic to proteins in the flea’s saliva, and they can show a severe skin reaction, even from one flea bite. The itching can be intense, and cats will often lick and chew excessively at their skin, especially around the base of the tail. Fortunately, there are now many topical flea-control products that are designed to kill fleas as soon as they jump on a cat, before they get a chance to bite, giving relief to most flea-allergic kitties.

Scratch, vomit, diarrhea

Adverse reactions to food may manifest themselves via the skin. In cats, the most common foods associated with food allergy include chicken, fish, beef and dairy. Even if a cat has been consuming an ingredient for a long time, he can still develop an allergy to it later in life. Severe generalized itching, miliary dermatitis, localized itching around the head, neck, ears and face, and self-inflicted hair loss due to over-grooming may be seen. A few cats will scratch so much that they cause trauma to their skin, and a bacterial skin infection may develop in the traumatized areas.

Some cats with food allergy develop gastrointestinal signs such as vomiting and/or diarrhea. These gastrointestinal signs can occur with or without concurrent skin symptoms.

Dietary elimination trials, in which the cat is fed a diet containing a protein source they haven’t encountered before (such as duck, rabbit or venison) are necessary to obtain a definitive diagnosis. Most veterinary offices sell prescription diets that contain proteins that are new to the cat. There are also prescription diets in which the protein has been hydrolyzed (pre-digested) into molecules that are too small for the immune system to recognize.

These dietary trials require patience on the part of the owner, as it may take anywhere from three to 12 weeks before improvement in the skin is noted. Cats who only experience gastrointestinal signs from their food allergy often show improvement much more rapidly when fed a hypoallergenic diet. Once a diet is found that resolves the cat’s symptoms, the cat will need to be on that diet long-term. Avoid cat treats should be avoided, as they might contain a protein source that triggers the reaction.

The ideal treatment for allergies is to avoid the allergen. This may be possible with allergic contact dermatitis, food allergy and flea allergy but may be difficult or impossible with inhalant allergy. Fortunately, there are numerous treatments and medications available for allergic conditions in cats, allowing our feline companions to live much more comfortable lives.