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This allergic cat was licking its hair off because it was itchy. Photo by VIN Dermatology Consultants

You or someone you know may have allergies, but did you know your cat can too?

Atopic dermatitis (atopy, allergic dermatitis, feline atopic skin syndrome, non-flea, and non-food hypersensitivity dermatitis) is a hypersensitivity, or over-reaction, to a variety of common and otherwise harmless substances in the environment. Cats with atopic dermatitis can be allergic to plant pollens, house dust, mites, and mold spores.   

Signs

Atopic cats may lick, chew, rub, or scratch parts of the body, such as the back, sides, face, and ears. This itchiness (pruritus) and scratching can cause thickened, reddened skin with excoriations (scratch marks) and crusts (scabs). However, atopic cats may also hide scratching behaviors. It’s very common for pet owners never to see their atopic cats scratch and instead only see alopecia (hair loss).

Diagnosis

Many conditions besides allergies can cause your cat to be itchy. To diagnose your cat, your veterinarian may take skin and hair samples to determine if a skin infection or parasite is causing your cat’s itching.

Once your cat’s veterinarian has ruled out other causes of itching and diagnosed atopic dermatitis, allergy tests can be used to identify what your cat is allergic to in the environment. Cats can be allergy tested through an intradermal allergy test or blood allergy test. In an intradermal allergy test, small amounts of common allergens are injected into the skin, and then the veterinarian watches for a skin reaction. In a blood allergy test, antibodies (protein levels) against various allergens are measured. Neither of these tests can diagnose atopic dermatitis. Instead, these allergy tests are used to identify what a cat is allergic to so that a cat can be started on allergen-specific immunotherapy (hyposensitization or allergy injections). 

Each allergy test has its advantages and disadvantages. Intradermal allergy testing is a specialized test performed by a board-certified veterinary dermatologist. A mild sedative is given to relax your cat during the test, and hair is clipped on one side of the chest. While a blood allergy test only needs a blood sample from your cat, some atopic dermatitis cats don’t have antibodies that the blood test can measure. Unlike humans, allergy tests cannot be used to diagnose food allergies in cats.  

Management

Cats with atopic dermatitis can’t avoid everything they’re allergic to. When cats groom themselves, they lick off and swallow allergens that have settled on their hair coat. For allergic cats, even a small amount of allergen can trigger a feeling of itch.  

If your cat is diagnosed with atopic dermatitis, a variety of anti-allergy medications are available. These medications include antihistamines, steroids (cortisone), and cyclosporine. Not every medication works for all cats. It can also be a struggle to give oral medications to some cats. Although steroid injections can be administered to cats, these injectable steroids may have more side effects than oral steroids. 

Not every medication works for all cats. With anti-allergy medications such as steroids, some cats may develop serious side effects.  

Another option to prevent flare-ups of atopic dermatitis in cats is allergen-specific immunotherapy, which involves hyposensitization and allergy injections. Immunotherapy involves giving your cat a series of diluted allergens based on what they are allergic to. Over time, immunotherapy makes cats less sensitive to their allergens. However, it takes time to have its full effect. Do not discontinue immunotherapy on your own without consulting your veterinarian. When helpful, immunotherapy is usually continued lifelong but may be given less frequently over time.