FLEA ALLERGY DERMATITIS
Also Known As: Flea bite hypersensitivity
Transmission or Cause: When a flea sucks blood from a pet, it passes its saliva
into the animal’s skin. Animals that are allergic to flea allergen will experience swelling,
irritation, and itchiness. When the animal scratches the bites, further trauma to the skin
lesions, hair loss, and more intense itchiness will result. A single flea bite can cause these
symptoms in an allergic pet; animals without this allergy must be bitten many more times
before their skin becomes irritated.
Affected Animals: Any breed or sex of dog can be affected. The average age for flea
allergy is three to five years. Cats also can be allergic to fleas.
Overview: Animals that have flea allergy dermatitis are hypersensitive to the saliva
a flea passes into the skin when it bites. The bite from a single flea will have a minimal
affect on a normal animal, but animals with flea allergy will experience immediate itching,
redness and swelling. It is the animals themselves, and not the fleas, that typically do
the worst damage. When an animal scratches its fleabites excessively, hair loss and skin
abrasions can result. Some animals will develop circular, red, painful sores called hot spots
that can occur anywhere on the skin, but commonly are seen along the back and tail base.
The most common allergic skin disorder, flea allergy only can be resolved by preventing
the animal from being bitten by the flea and removing all the fleas from the animal’s
environment. There are medications available, however, that will alleviate the itching and
discomfort until complete flea control is achieved.
Symptoms: Common findings in an animal that is allergic to fleas include increased
scratching or itchiness, loss of hair, hairs that appear broken, crusts and erosions of the
skin, and pimple-like bumps. Thickened skin with darkened areas can be seen in severe
cases. Fleas or flea feces, which can be difficult to detect, indicate the presence of fleas.
Hot spots sometimes can be seen along the dog’s back and tail base. These sores are
usually circular, red, oozing, and very painful, often requiring medical attention.
Description: Flea allergy is the most common allergic skin disorder, affecting animals
with an abnormal sensitivity to the saliva a flea injects into the skin when it takes a blood
meal. In reaction to flea allergen, allergic animals will have inflammation and irritation of
their skin, not to mention intense itchiness. Hair loss and skin lesions can result when an
animal scratches or bites its irritated skin.
The problem may last year-round in warm climates or in flea-infested indoor environments.
In regions with cold winters, the allergy will appear seasonally during the warm months
of the year. Treatment of flea allergy requires eliminating the fleas from the animal, other
pets, and the surroundings. Various medications can provide temporary relief of itching for
severely affected animals until flea control is achieved.
It may be difficult to detect fleas on a pet, but brushing it over a white sheet may help:
flea feces, a dark, black material, that falls from the animal’s hair onto the sheet would
suggest the presence of fleas. A flea comb also can be used to look for the feces or the
fleas themselves. Pets should be examined often if itching is noted.
Diagnosis: The symptoms of flea allergy can mimic other disorders of the skin. Before
concluding that an animal is allergic to fleas, the examining veterinarian first will attempt
to rule out allergies to food and inhalants, internal parasites, drug reactions, hair follicle
inflammation (folliculitis), fungal infection, and other topical parasites, all of which may
have signs similar to an allergic reaction to fleas. A thorough history and physical exam
will be required, during which the veterinarian will analyze the type and size of the skin
lesions.
It is often very beneficial for pets with suspected allergies to be tested for allergens
that may be causing the animal to be itchy and uncomfortable. There are two common
techniques that veterinarians can use to determine any underlying allergies to allergens
such as fleas. One technique is called intradermal skin testing which requires the injection
of different allergens into the skin. This usually is done by a veterinary dermatologist and
may require sedation. The second technique involves taking a blood sample and sending it
to a laboratory for allergy testing. This is called serologic allergy testing. There are varying
opinions about serologic testing, so consultation with the examining veterinarian will be
necessary.
Prognosis: An animal with flea allergy dermatitis will always remain allergic to fleas.
The severity of this allergy typically worsens as the pet ages. If fleas are eliminated
from the animal’s environment, the pet will stop suffering the symptoms of flea allergy.
If the response is incomplete but flea control has been achieved, the animal should be
reevaluated by the veterinarian for concurrent allergies.
Treatment: The goals of treatment are to alleviate the animal’s allergic reaction to
fleas by preventing the flea from biting the animal and eliminating the fleas from the
environment. It is very important that owners completely remove the fleas and their eggs
from the animal’s environment. This involves the treatment of all household animals for
fleas to prevent the allergic pet from becoming reinfested. There are many commercially
available products that kill fleas both indoors and outdoors. Additional products have been
designed for use on the animal. Professional pest extermination companies, which usually
carry a satisfaction guarantee, are also an option. A veterinarian can customize a flea
control program to meet an allergic pet’s individual needs.
Therapy for the allergic reaction is based on the severity and history of the symptoms.
Following an evaluation of the dog, the veterinarian may prescribe any of the following
medications: topical treatments, medicated shampoos, steroids, antihistamines, antibiotics,
and fatty acid supplements such as skin oil replacement. The examining veterinarian often
will recommend a commercially available product that kills fleas on contact, before they
have a chance to bite. These products are ideal in helping prevent further flea allergic
reactions.
The effectiveness of allergy shots, or hyposensitization, for treating flea bite hypersensitivity
remains controversial. This method of treatment, prescribed by a veterinary dermatologist,
usually is reserved as a final therapeutic step for severely afflicted animals not responding
to strict flea control.
Prevention: Prevent fleas from entering the household. If evidence of fleas is noted on
the dog or on any other pets in the household, early intervention can stop the problem
before the symptoms become severe.
