Author: Casey Stepnik, DVM, DACVD
(Board-Certified Dermatologists)

“Flea allergy dermatitis! That’s impossible! I’ve NEVER seen a flea on my pet!” This is a common response from owners whose pets have just been diagnosed with this hypersensitivity reaction. Flea allergy dermatitis (FAD) is not a flea infestation. Likely you nor your vet have ever seen evidence of fleas on your pet. Surprising for most owners to hear, every healthy pet will have intermittent flea exposure, no matter where you live. In fact, intermittent exposure to fleas rather than true flea infestation contributes to the development of flea allergy dermatitis.

The most common flea to cause problems for the dog and cat is the flea, Ctenocephalides felis. Fleas are not just carried on dogs and cats, they are also carried on wildlife, such as raccoons, opossums, foxes, and coyotes, just to name a few. When a flea-carrier passes through your yard, your neighborhood, or areas that you may frequent with your pet (such as dog parks & grooming facilities), flea eggs will roll off the animal carrier into the environment. The flea life cycle is completed in the environment with the life cycle arresting in the cocoon stage. Adult fleas will emerge from their cocoons when a suitable and preferred host (ie. dog or cat) is nearby. Adult fleas are small, wingless, blood-sucking insects. Adult fleas are capable of biting 30-40 times per hour! When an adult flea bites a pet, it injects saliva into the skin. Flea saliva contains many allergy-producing proteins. Patients that are hypersensitive to these proteins will develop symptoms of flea allergy dermatitis.

So what is flea allergy dermatitis? FAD is an allergic reaction to flea saliva that occurs in our companion animals after they are bitten by an adult flea. As previously stated, it more commonly develops in pets that are only intermittently exposed to fleas rather than infested. Diagnosis of flea allergy dermatitis is a clinical diagnosis based on compatible history, clinical signs, and response to treatment. Symptoms of FAD may occur year-round with seasonal worsening in the summer and fall. In certain geographic locations, flea allergy dermatitis is the most common allergic reaction diagnosed in both dogs and cats.

Flea allergy dermatitis can develop at any age, in any breed, and any gender. Dogs with flea allergy dermatitis will be extremely itchy on their rump, flanks, tail and groin area. They may exhibit “corn-cobbing” behavior which is a quick, nibbling behavior directed at those areas. FAD is the most common trigger for pyotraumatic dermatitis, commonly called “hot spots”. Cats with FAD will often develop small crusted lesions, called miliary dermatitis, on their head, neck, rump, thighs, and abdomen. Cats will often overgroom their abdomen to the point of complete hair loss.

Successful management of a patient with FAD can be multifaceted and may require the help of a board-certified veterinary dermatologist.