Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Fleas: The Allergy Machine

Pet Column for the week of August 29, 2011

Related information:

Related site - Dermatology Services at the Veterinary Teaching Hospital
Services - Dermatology

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Brittany Way Rose
Information Specialist

Most pet owners know that dogs and cats should be treated regularly with medication to prevent an infestation of fleas, but they may not realize that even a pet receiving a flea preventive can be bitten by an adult flea and develop an allergic reaction.

Dr. Domenico Santoro, a veterinary dermatologist at the University of Illinois Veterinary Teaching Hospital in Urbana, says that flea allergic dermatitis represents the most common cause of allergies in temperate climates.

"Many pets are allergic to the saliva of the adult flea, which is injected into the skin when the flea bites to enjoy a blood meal," says Dr. Santoro. "If your dog is allergic, you will likely notice itchiness and sores on the rump, tail base, thighs, and lower abdomen. In cats you may see itchiness around the neck."

Even if your pet isn't born with an allergy to fleas, it is possible to develop this allergy, according to Dr. Santoro.

You may notice your pet scratching more in the summertime. Unfortunately, the flea problem knows no season.

"Fleas can survive in all kinds of temperatures, so fleas—and flea allergy dermatitis—are present year-round," says Dr. Santoro. "However, the hot and humid conditions in summer facilitate the development of flea larvae, so the number of fleas in the environment may be higher in summer."

What if you don't see fleas on your pet? Or even flea excrement, which has a characteristic "comma" shape?

"Often the animals with the worst allergies to fleas spend a great deal of time grooming and chewing and may ingest the fleas and flea dirt," explains Dr. Santoro. "Even a small number of fleas could trigger an allergic reaction, so you may not be able to find any on your pet."

Of course, prevention is the best way to fight flea allergic dermatitis. Anti-flea medications for animals with allergies are very important and will help prevent an allergy flare up.

If your pet does develop allergies even while on preventives, your veterinarian may prescribe a course of medication such as glucocorticoids to ease your pet's itchiness.

If the problem is persistent it is most likely an environmental problem and you may want to treat your house or room with sprays or spot-on formulas. Use only products that have been recommended by your veterinarian to ensure that the formulations aren't toxic to your pets.

Flea allergic dermatitis can be very annoying to your pet and may even lead to skin infections if untreated. If your pet is itchy, be sure to ask your veterinarian for advice.