What to do About Pets with Allergies

When your dog pumps its leg frantically to scratch its ear, or your cat bites its tail furiously until the fur falls out, it's clear that your pet is itching for relief.

Occasional scratching is normal, but if a pet scratches or bites itself relentlessly, a health problem may be the cause. Itching can be triggered by a variety of conditions, ranging from liver disease to lice, from fungus to fleas, from mange to anxiety. But the leading cause of itching and scratching in pets is allergies, says Linda Messinger, D.V.M., a board-certified veterinary dermatologist at the Veterinary Referral Center of Colorado in Englewood. "Allergies are also the most common underlying cause of ear problems in dogs," she adds.

Unlike people with allergies, animals don't usually get stuffy or runny noses or watery eyes. Their main symptom is itchy skin, which can turn raw and red from scratching, licking, and chewing. This condition is called allergic skin disease, or allergic dermatitis. With enough scratching and biting, open sores can form, creating a haven for bacteria or yeast that can lead to infection.

"Just about every mammal can get allergies," says Lisa Troutman, D.V.M., a veterinarian with the Food and Drug Administration. "So can hamsters, rabbits, birds, and some other pets." But dogs and cats are the pets most frequently seen with allergies.

To relieve the itch, dogs may scratch and bite at themselves and rub their face with their paws or against the floor and furniture. "Cats tend to pull out their hair and get patchy hair loss on their ears, legs, and around their eyes," says Troutman. "They'll make themselves bald."

There is no cure for allergies. "They are a lifelong problem," says Messinger, "and oftentimes they get worse as a pet gets older."

But there are treatments to relieve itchiness, clear up infections that arise from constant scratching, and even "desensitize" a pet to substances that cause allergies. In addition to regulating drugs for people, the FDA regulates drugs for animals, and the agency's Center for Veterinary Medicine has approved medications to treat itchy pets and their infections.

The key to making your pet comfortable is to find out the cause of the itchiness. If the pet is allergic, determining the source of the allergies will help with treatment, says Messinger.

Types of Allergies

Allergies that can plague pets are grouped into four types: flea, food, atopic, and contact.

The most common type of allergy in both dogs and cats is flea allergy. The offending allergen is actually the protein in flea saliva left in the skin after a fleabite.

Atopic, or inhalant, allergy is the second most common allergy in dogs and the third most common in cats. Breathing in or directly contacting airborne particles in the environment, such as mold spores, dust, tobacco smoke, and pollens, will activate atopic allergies.

If a pet is allergic to pollens, it will show symptoms even if you keep it indoors, says James Jeffers, V.M.D., a board-certified veterinary dermatologist at the Animal Allergy and Dermatology Clinic in Gaithersburg, Md. Outside airborne substances waft their way into the house, and air filters don't tend to bring relief to pets with these types of allergies, he says.

Although pets with atopic allergies sometimes have respiratory problems, such as coughing and sneezing, they more typically develop itchy skin. Certain dog breeds are more likely to develop atopic allergies, including terriers, Dalmatians, and golden and Labrador retrievers.

Food allergies are the second most common type of allergy in cats and the third most common in dogs. Food ingredients most likely to trigger allergies in cats are fish, milk, beef, and eggs. Ingredients most likely to cause a reaction in dogs are beef, soy, chicken, milk, corn, wheat, and eggs. Some pets with food allergies may have vomiting and diarrhea.

A reaction to physically touching a substance is called contact allergy, the least common type of allergy in dogs and cats. Contact allergens include grass, wool, and plastic. Jeffers occasionally sees dogs in his clinic with "plastic dish dermatitis," an irritation to the skin on the nose caused by a reaction to an antioxidant found in a plastic food or water dish. The condition clears up when the pet is switched to a metal or ceramic dish. And although uncommon, some cats become allergic to kitty litter, says Jeffers. But allergies caused by contact with chemicals, such as those contained in cleaning fluids, waxes, carpet cleaners, and lawn fertilizers, are "about 1 in a million," he says. Nevertheless, these products are potentially toxic, and pets should be restricted temporarily from areas treated with them.

Diagnosing Pet Allergies

There are many conditions that can make a pet itch or have hair loss, including endocrine, autoimmune, infectious, and parasitic skin diseases. It takes some detective work to identify the cause. A veterinarian may be able to diagnose the problem or may refer your pet to a veterinary dermatologist, a specialist in treating skin conditions in animals.

If allergies are suspected, the first thing a veterinarian will usually ask is if the pet is on a flea-control product, says Troutman. Flea allergies are the most common type of allergies and the easiest to control, she says. And just because a pet is kept indoors doesn't mean it can't have fleas. An owner might bring fleas into the house on a piece of clothing, and the fleas can jump onto the pet. Just a single fleabite can cause an allergic animal to itch severely for more than five days, according to the American Animal Hospital Association.

Pet owners have many options for flea control on pets and in their environment. Veterinarians can recommend an appropriate product. (See "Taking the Bite out of Fleas and Ticks," July-August 2001 FDA Consumer.)

Once flea allergies are ruled out and if the itch is non-seasonal, food allergies are checked next. Food allergies are not related to a season, while many atopic allergies start out as a seasonal problem, says Morris. Dogs and cats that develop atopic allergies usually show symptoms between 1 and 5 years of age, he says, but food allergies can crop up at any time. They are high on the list of suspects when a dog or cat first exhibits itchy skin at an age less than 6 months or over 5 years.

To test for food allergies, the pet is put on an "elimination diet" for at least 10 weeks, which means it is fed food that consists of a protein and carbohydrate that the pet has not eaten before, such as duck, venison, and potatoes. Veterinarians offer these special foods, and some may be found in retail stores. Or the owner may choose to feed the pet a homemade diet of foods recommended by the vet.

If the animal's itching subsides by at least half, the allergen is considered to be one or more food ingredients, says Jeffers. To confirm this, the owner can reintroduce the old food to see if the symptoms return. To find the specific ingredients that trigger the allergy, the owner should feed the special diet again and add one ingredient at a time from the old diet for at least a week until the itching increases, indicating that the last added ingredient is an allergen. Or the owner may choose to stay with the special food to avoid causing the pet discomfort each time an allergic ingredient is fed.

While the pet is being tested for food allergies, it should not be given treats, chewable medications, table scraps, or rawhide toys that may contain an allergen.

To check for atopic and contact allergies, veterinary dermatologists use an intradermal allergy test, or skin reaction test. The pet is mildly sedated, a postcard-sized area on the side of the pet is shaved, and small amounts of potential allergens are injected into the skin on the shaved area. If the pet is allergic to a particular substance, the skin will become inflamed at the area of the injection.

Treating Allergies in Pets

Although allergies can't be cured, they can be controlled by avoiding the allergens, treating the symptoms, or desensitizing the pet.

Fleas, food ingredients, and some substances that trigger contact allergies may be avoidable, but "with atopic allergies, avoidance is virtually impossible," says Jeffers.

Drug products are available to relieve the symptoms of itchiness and inflammation in pets. Like any drugs designed for animals, these products must obtain FDA approval before they can be marketed by meeting rigorous scientific standards similar to those for human drugs. Veterinarians often prescribe antihistamines approved by the FDA for humans to relieve itchiness in pets. Under the Animal Medicinal Drug Use Clarification Act of 1994 (AMDUCA), veterinarians may legally treat dogs and cats with drugs that have been approved for people but not for animals. Pet owners should check with their veterinarians before giving a pet any human medications, including over-the-counter antihistamines.

"If we can control the allergies through medication for occasional flare-ups, antihistamines and steroids are useful," says Troutman. But if these medications are needed continuously to provide relief, Troutman recommends seeking other options, such as immunotherapy.

Immunotherapy is a treatment that stimulates the immune system to decrease the body's reaction to allergens. Similar to people with allergies, animals can be given immunotherapy, or desensitization injections. These "allergy shots" contain small amounts, or extracts, of the substances that the animal is allergic to, based on the results of skin testing. The owner gives the shots to the pet at home, usually in the scruff of the neck. The extracts used for allergy testing and treatment in veterinary practices are licensed by the U.S. Department of Agriculture's Center for Veterinary Biologics.

Allergies in pets are neither preventable nor foreseeable, says Morris. "You can have one puppy out of a litter of 10 with allergic skin disease, or it can skip generations. We can't possibly predict it," he says, even if you have a pet examined by a vet at a very young age.

To find a veterinary dermatologist: American College of Veterinary Dermatology

Article by Linda Bren. (FDA

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