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Flea Control and Flea Bite Allergies

Flea bite hypersensitivity and flea allergic dermatitis (FAD) is a skin disease that affects many animals, including cats and dogs. It is often considered to be the most common skin disease in pets. The allergy is an immune response to the saliva (or components of the saliva – including antigens, amino acids, aromatic compounds, polypeptides, and phosphorus) injected by fleas when they bite your cat or dog. The bitten animal’s body begins an exaggerated antigen-antibody reaction to the saliva, inflammation results from scratching by the pet and secondary bacterial infections (principally Staphylococcus intermedius and Malassezia pachydermatis) can begin if the skin is traumatized by the scratching. Flea allergy can develop in your pet at any age, although, 61% of of flea-allergic dogs develop FAD between 1 and 3 years of age. It is uncommon for hypersensitivity to develop in very young animals (less than 6 months of age) because they do not yet have a fully developed immune system to react to the flea bite.

The flea life-cycle is the typical 4-stage process of the adult flea, egg, larva and pupa. Adult fleas must feed on blood (from your pet) before they can reproduce. Once the adult flea lays her eggs on the host (usually in batches of approximately 20), these fall to the ground and frequently into the animal’s bedding. The adult flea may also jump off the host after laying the eggs, however, adults cannot survive long once they are off your pet. Both the egg and larval stages live in the environment rather than on the animal, therefore, it is essential to treat both the animal (for the adults) and its environment.



The most obvious symptom of flea bite hypersensitivity and FAD is severe itching of the skin, which your pet attempts to cope with by scratching and biting. At this stage, the condition is referred to as pruritis, which in hypersensitive animals can be caused by as few as one or two flea bites a week. Because of the low numbers of fleas which can cause the condition, symptoms often persist, even after flea control methods have been used. Symptoms will often occur in episodes, and in general, symptoms worsen with age. Scratching can become habitual and develop into a condition called neurodermatitis in which affected skin become become thick and leathery. After frequent scratching has been occurring for a while, the most notable symptoms are the patchy loss of hair, erythema (redness of the skin), pustules (pus-filled bumps) and crusts or scabs on the skin. Although any part of the body can be affected by flea bite hypersensitivity, the hind end is often affected more than the front or head of your pet’s body.


One problem with diagnosis of FAD is that it may be difficult to see fleas or flea dirt (flea feces). This is partly because the pet’s scratching has likely removed them. Carefully inspect your pet’s skin by using a flea comb to part the fur. This will enable you to inspect for fleas or flea dirt more readily. There are skin tests available for mites or bacterial skin diseases, and these may be recommended by your veterinarian if fleas cannot be seen directly. The distribution of scratching or lesions on the pet’s body can assist in diagnosis. Sometimes, the best diagnostic method is to simply treat for fleas and observe for changes in the symptoms.


For animals with flea bite hypersensitivity, it is essential to control the flea population on the animal, in its environment, and prevent any re-occurrence. There are numerous commercial applications for killing adult fleas, however, these only act for a period of time and all should be repeated as indicated on the product for effective and continuous flea control. Spot-on insecticides are often used. These are a topical treatment, usually applied to a small area, (e.g. the back of the neck) where the animal is unable to lick it. Oral products are also available, but some of these can be difficult to administer, especially to cats. Shampoos can be especially beneficial for young animals or for a severe and acute flea infestation, however, it is essential that a more long-term product is also used to ensure continuous flea management. There are also many commercial products available that can be used to treat for flea eggs and larvae. If the treatment causes fleas to leave the host pet, the fleas may bite humans during the process of searching for another host. It is virtually impossible to successfully control fleas in the long-term if your pet is kept outdoors. There are some products that may be effective for sort-term control, but this is dependent on the kennel or other housing not becoming infested. If your pet is allergic to flea bites, they may require steroids or anti-histamines to reduce their sensitivity. Similarly, if a bacterial infection develops from any lesions, your pet may require antibiotics. Your veterinarian may request follow-up examinations to assess the progression and success of treatment they have recommended.


The most essential factor in successfully controlling or treating fleas is the application of regular doses of flea treatment. This should be done at the frequency recommended by the manufacturer, or as advised by your veterinarian. It takes only one or two bites for an animal that is allergic to fleas to start itching. Therefore, it is best to be consistent with flea control products and the timing of their application. You should also consider other factors such as how frequently your pet is bathed or swims, and whether you are using topical or spot-on treatments. This will determine the time between applications.

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