Inhalant Allergies Target the Skin

Sneezing and watery eyes can result, but sufferers will more often develop itching, hair loss, sores and infections

Your cat is scratching, licking away sections of fur. His head, neck and ears itch. With the arrival of spring, you might suspect a flea infestation, but more likely allergies to airborne substances could be to blame. The usual suspects — pollens, molds and dust mites — can cause inflammation of the skin called feline atopic dermatitis (AD).

What starts as a seasonal allergy can become a year-round condition, resulting in intense itching, self-induced hair loss, sores and infections. Like hay fever in humans, AD can cause sneezing, watery eyes and ear infections in cats, “But the skin is always the main target,” says dermatologist William H. Miller, VMD, Medical Director of the Cornell University Hospital.

Unclear Origin.

“In dogs, AD is a contact dermatitis, where the allergen binds to the skin and triggers the allergic reaction. Since cats are, in general, hairier than dogs, the contact route of exposure doesn’t explain their disease entirely,” Dr. Miller says, adding that cats’ grooming pollen off their skin and inhaling allergens also have to be considered.

While an estimated 10 to 30 percent of dogs suffer from atopy, the incidence in cats is unknown. In his five-year study of 194 feline dermatology patients, Dr. Miller found atopic dermatitis in 14 percent of cats.

Diagnosis presents a challenge. Because atopy and food allergy signs are similar, “the only real way to prove that an animal has AD is to make sure he doesn’t have a food allergy, and that involves strict dietary manipulation,” says Dr. Miller. That can be difficult because cats often resist changes in diet. “However, by carefully reviewing the patient’s history and the patient himself, we typically know whether the cat has AD or a food allergy.”

Allergies are caused by the body’s immune system overreacting to triggering substances called allergens. This usually leads to atopic dermatitis, with some pets with severe allergies requiring lifelong treatment. Four main skin reactions characterize AD in cats:

– Facial pruritus (itching) and traumatic alopecia (fur loss) in which the cat starts itching at normal skin and creates the lesions we see, Dr. Miller says.

– Miliary dermatitis and eosinophilic granuloma complex. “In these, lesions appear spontaneously and then the cat responds to them. To make it more challenging, some cats have multiple forms all at one time.”

Asthma caused by allergies to inhaled environmental allergens is a different condition, affecting up to five percent of cats, says University of Missouri researcher Carol Norris Reinero, DVM, Ph.D. Signs include coughing, wheezing and difficulty breathing. “Feline asthma is a common disease often mistaken for other respiratory diseases, but it is truly an allergic reaction to something in the environment that is innocuous to others,” she says.

Owners should consult a veterinarian whenever respiratory or skin reactions occur. “Atopic dermatitis is forever,” Dr. Miller says. “Many cats are easily managed with relatively safe medications. But some can continue to worsen each year and require a very intense management regime.”

A detailed medical history, physical exam and restricted diet can eliminate food, fleas and diseases as the reason for a cat’s dermatitis. Identifying specific environmental allergens involves allergy testing. “Allergy testing isn’t foolproof,” Dr. Miller says. Allergy tests show that a cat has antibodies to specific substances, which means only that he has been exposed and reacted to ragweed or dust mites, for example.

Blood and Skin Tests.

Antibodies are detected two ways: in the blood with blood or serologic allergy testing or on the surface of mast cells (white blood cells found in connective tissue) by intradermal skin testing. Many factors affect the accuracy of both allergy tests, so testing is recommended only if specific-allergen densitization treatment is planned.

“We usually allergy test animals only for environmental allergies when avoidance and medical management don’t provide satisfactory results,” says Dr. Miller. “There is no real benefit to testing unless you are going to use Allergen-Specific Immunotherapy (ASIT).”

Immunotherapy, administered orally or by vaccine, uses individually-tailored allergen mixtures to desensitize the immune system not to overreact to those substances. The therapy is successful in 50 to 75 percent of cases. In Dr. Miller’s retrospective study, about 90 percent of the allergic cats treated with ASIT improved.

The first step in managing feline AD is to eliminate or reduce known allergens in the cat’s environment. Medical options include fatty acid supplements, topical and oral steroids, antihistamines and the immunosuppressant drug cyclosporine A. Antibiotics and antifungal drugs treat secondary skin infections.

Anti-inflammatories, including glucocorticoids like prednisolone, are often prescribed. Cats generally have few adverse reactions to long-term steroid use, but these can include increased thirst and urination and a weakened immune system.

Dr. Miller prescribes ASIT frequently because Cornell primarily treats severe cases of year-round AD. Animals with milder or seasonal atopy may benefit from antihistamines or supplements with balanced omega-3 and omega-6 fatty acids.

The complex mechanisms that cause AD in cats and dogs are unclear, but in humans, itching is often triggered by histamine, a chemical produced by mast cells as an immune response. Antihistamines, such as chlorpheniramine and cetirizine, are considered more effective for AD in cats than in dogs and safe if doses are small enough. “Antihistamine overdose can cause hyper-excitability in cats, which can be detrimental if the cat has heart disease or another internal disorder,” says Dr. Miller.

Current research on new therapies focuses mostly on dogs but, “As the science of allergy in animals advances,” Dr. Miller says, “new treatments for the atopic cat will become available.”