The term "allergy" is a general reference to an immune-mediated hypersensitivity reaction to some antagonizing environmental "allergen," which is normally innocuous to non-allergic animals. A more specific definition of "allergy" is an altered reaction to something (the allergen) following a second or subsequent exposure to it. Virtually anything in the environment can be an allergen.
How Skin Allergies Affect Cats
Once a cat has been exposed to an allergen, subsequent exposure to the same substance will cause hypersensitivity (allergic) reactions, depending upon the particular cat's immune make-up. Most allergic reactions in cats cause some degree of skin irritation; the skin becomes inflamed, severely itchy (pruritic), irritated and red. Owners often report rashes, licking, scratching, biting, restlessness, pustules or bumps on the skin, "hot spots" where the skin becomes raw and infected from self-trauma, sneezing, red watery eyes, excessive grooming and generalized lethargy. Cats seem to be most commonly affected in the groin or flank area, on the paws, between the toes, in the ears, in the axial area (armpits) and under the neck. Secondary bacterial and yeast infections often occur, especially in the ears, accompanied by a foul, yeasty odor. Cats with food allergies can have gastrointestinal disturbances in addition to skin irritation, such as burping, vomiting, diarrhea, flatulence (excessive production of intestinal gas), weight loss, hives and enlarged lymph nodes.
Depending upon the inciting cause, allergic cats usually begin to develop clinical signs before the age of two. These signs are often seasonal and may disappear in the winter, only to return with a vengeance during hotter months of the year.
Causes of Feline Skin Allergies
Most feline allergies are hypersensitivity reactions to flea or tick bites, contact or airborne inhalants or some ingredient in their food. The inciting contact with the allergen can be by touch, inhalation, injection or ingestion. Allergies to fleas, which are quite common in cats, are caused by an immune-mediated hypersensitivity reaction to flea saliva, which leads to irritation and itchiness at the site of a bite, increasing the risk of secondary bacterial infection and localized hair loss. Common contact and inhalant allergens include seasonal pollen, trees, bushes, grasses, weeds and flowers. These allergies, in cats and in people, are sometimes referred to as "hay fever." Food allergies can be a reaction to essentially anything in a cat's diet. Some common food allergens include beef, dairy products, wheat, eggs, chicken, lamb and soy. Cats also can develop allergies to indoor or outdoor mold spores, dust mites, household cleaners and chemicals, drugs or a number of other environmental allergens.
Why some cats are so terribly affected by skin allergies while others are not is unclear. There seems to be a genetic predisposition to developing allergies, since the condition often occurs in littermates or in the offspring of cats that suffer from allergies. Skin allergies may also be linked to stress or systemic medical disorders. Cats that are particularly anxious or fearful may be prone to developing skin allergies, and cats that are in poor health may also succumb to skin allergies more easily.
Preventing Allergies in Cats
The best way to prevent allergic reactions in companion cats is to prevent their contact with (or inhalation or ingestion of) whatever is causing the hypersensitivity. For example, flea bite allergies are best prevented by removing the allergen – fleas – from the cat's environment. There are a number of good topical products to keep fleas off of our pets, including medicated collars and topical liquid treatments and preventatives, among others. To prevent hay fever, owners should keep their affected cats away from whatever seasonal allergen is causing the problem. Food allergies can be prevented once the causative dietary component is identified, which can be done through an elimination diet supervised by a veterinarian. A number of commercial kibbles containing novel protein sources are available for cats that are allergic to more traditional protein sources.
Feline skin allergies can be difficult, but not impossible, to diagnose and manage. Veterinarians use a combination of a thorough medical history, comprehensive physical examination, blood and/or skin tests and assessment of the cat's response to treatment to identify and control allergic reactions. Cats with skin allergies have a variable prognosis – again, depending upon the underlying cause of the condition. In many cases, the allergies will resolve with effective flea/parasite control, special diets and/or medicated topical treatments. Unfortunately, sometimes the precise cause of the allergy remains elusive.
Despite the many different causes of skin allergies in cats, the symptoms of skin allergies are most often the same. The symptoms are usually seasonal, and they usually appear at a young age.
Symptoms of Skin Allergies in Cats
The two most common symptoms of skin allergies in cats are continual licking and constant scratching. The licking is usually focused on areas which include the groin area, the base of the tail, and the sides. If the allergies are not treated, the cat will lick itself so much that these areas begin to appear bald. Constant scratching occurs most often around the ears, neck, and head area.
As a cat suffering from skin allergies constantly licks and scratches itself, sores will begin to appear around these areas. The severity of the sores depends on how much the cat is scratching and licking in an effort to relieve the constant itching of the skin.
If a cat is suffering from severe allergies, small puss filled bumps may begin to appear around the head and neck area, and in extremely severe cases these bumps can occur over the entire body. In cases where a cat is experiencing symptoms of skin allergies due to a food allergy, periodic vomiting and diarrhea may also occur.
Cats that suffer from skin allergies often develop secondary bacterial or yeast infection on their skin and in their ears. Excessive ear discharge, and an odor coming from the ears and body, can occur if these secondary infections develop. The cat may also have a greasy feel to its body, and the fur may appear sticky and patchy.
Anyone who has seen a cat constantly scratching or chewing on itself probably has seen a cat with skin allergies, which medically are referred to as "atopy" or "atopic dermatitis." Whether caused by exposure to plants or pollens, flea or other insect bites or ingredients in food, skin allergies can cause mild irritation to dramatic sores from self-trauma and resulting secondary infections. The precise cause of feline skin allergies is difficult, but usually not impossible, to diagnose. Veterinarians have several tools at their disposal to assist them. These include observation of the cat's symptoms (especially whether they are seasonal), assessment of its response to treatment, standard blood work and elimination of other possible causes of the clinical signs. If an immune-mediated hypersensitivity reaction is suspected but confirmation remains difficult, a "patch test" series may be performed.
Diagnosis Based on Clinical Signs
Skin allergies in cats cause classic clinical signs, usually intense itchiness (pruritis). Many veterinarians are comfortable making a presumptive diagnosis of skin allergies based upon the cat's clinical presentation. If treatments to alleviate the cat's symptoms are administered and the problem resolves, no further tests should be necessary. For example, if a flea-infested cat is scratching vigorously to the point of self-trauma and the scratching goes away with appropriate topical and environmental treatment, it is reasonable to assume that the condition was caused by flea-bite hypersensitivity. Similarly, if a pruritic cat stops scratching with a change in the owner's laundry detergent, it is reasonable to consider that the prior detergent was the offending allergen.
Most veterinarians presented with a severely itchy cat will take a complete history and conduct a thorough physical examination, looking especially for evidence of external parasites, bacteria and/or yeast. They may take skin scrapings, examine plucked hairs microscopically and look closely at a number of samples taken from the ears and elsewhere on the cat's skin. Fungal cultures may or may not be appropriate.
Testing for Skin Allergies
A standard complete blood count, serum chemistry panel and a urinalysis are often used to screen for possible underlying medical conditions that could be causing or contributing to the cat's clinical signs. In atopic cats, unlike in dogs, the blood work often discloses a condition called "eosinophilia," which your veterinarian can discuss with you if necessary. Other laboratory tests also are available, including measurement of serum antibodies to particular allergens and an intradermal "patch test." The skin patch test involves injection of tiny amounts of a number of different allergens into the cat's skin, and observing and measuring the skin reaction (called a "wheal"), if any, to those distinct allergens. Skin biopsies can be taken to help rule out other causes of clinical signs as well, although biopsies will not reveal allergic causes.
If food allergies are suspected (they are fairly common in our companion animals and are especially probable if the cat's signs are nonseasonal), your veterinarian may recommend an elimination diet. In a nutshell, this means putting the cat on a bland diet with few ingredients (often rice and chicken), observing the cat's skin reaction, if any, to the food, and then gradually adding in other foods to assess how the cat reacts to them. This process can take many months, but if the cat is found to be allergic to certain food ingredients, the time is well spent.
Successful treatment of feline skin allergies initially requires pinpointing the cause(s) of the allergy and then eliminating the inciting allergen(s) from the cat's environment. If the allergen(s) cannot be removed or are never identified, medical treatments are available to help control the cat's symptoms. It is important for owners to work closely with their veterinarians to identify exactly what their cats are allergic to before attempting treatment. Allergies usually are a lifelong problem. The goal of therapy is to eliminate or at least minimize exposure to the inciting allergen(s), while at the same time managing the cat's comfort and maintaining its quality of life.
Treating Skin Allergies in Cats
Most skin allergies in companion cats are treatable. For example, if the cat's skin symptoms are caused by an immune-mediated hypersensitivity to flea saliva, the owner has many options available to eradicate that parasite from the cat's environment. Treatment options include monthly anti-parasitic medications that are applied to the cat's skin, together with treatment of all other animals and the carpet in the cat's living environment, as well. Cats with severe allergies to parasite bites may need to be kept exclusively indoors during the warm spring and summer seasons to prevent their allergic reactions.
If a cat is allergic to some environmental inhalant, the owner may be able to remove that substance from the home once it is identified. If grasses or pollens are the culprit, perhaps the owner will consider transitioning their indoor-outdoor cat to a completely indoor environment to easily resolve the problem.
Many topical treatments are available to soothe irritated skin, reduce inflammation and calm itchiness. These include shampoos, lotions, gels, rinses and other topical treatments that your veterinarian can discuss with you. Cool baths can help alleviate the symptoms of feline skin allergies as well, although many cats vigorously resist being bathed.
In cases of food allergies, the cat's diet obviously will need to be managed once the ingredients that cause the allergies are identified through dietary elimination trials. Owners may use homemade diets or can take advantage of the wide variety of specialized cat foods that are commercially available, including a number of kibbles with unusual protein sources such as salmon, venison or duck. Diets rich in essential fatty acids reportedly help many pruritic animals.
Antihistamines are commonly used to help alleviate the itchiness associated with feline skin allergies. Side effects of these drugs include sleepiness, lethargy, and sometimes nervousness and anxiety. When skin allergies cause severe symptoms that cannot easily be controlled, injectable or oral corticosteroids may be used short-term to calm the clinical signs and break the itch-scratch cycle. This treatment normally is reserved for severe cases, because long-term steroid use can cause debilitating side effects.
Advanced, long-term treatments are available to help adapt a cat's immune system to the particular allergens involved, again once they are identified. This involves subcutaneous administration of gradually increasing amounts of the inciting allergens, essentially to enhance the cat's tolerance of contact with those allergens. This type of therapy can take weeks to months to be successful, and maintenance injections should be given periodically to maintain the efficacy of the treatment.