Flea Allergy Dermatitis (FAD) results from an allergy to a protein in the flea saliva, which comes into contact with the pet when they get a bite from a flea. Dogs and cats with FAD may have a minimal flea burden. This is because after repeated exposure to the flea saliva, the animal can develop a hypersensitivity to the saliva and develop a severe skin reaction even after one bite from a flea. In dogs and cats that do not have FAD, they can often have a high flea burden with minimal signs or symptoms of clinical disease. However, in animals with FAD, even a few fleas can cause severe itching.

Dogs can develop red irritated skin with hair loss which is primarily concentrated over the rump, tail base and thighs. They are also extremely itchy. Cats may also be affected around the head and neck. Often these animals will cause a lot of self trauma through biting, chewing, scratching and rolling. Secondary infections are common.

A diagnosis of FAD is usually based on the location of skin lesions and the itch resolving after trialling flea control. While evidence of fleas or flea “dirt” (faeces) can help with the diagnosis, they are not always easy to find, especially in cats who groom themselves well.

Flea Allergy Dermatitis is best managed by ensuring the pet is on regular flea prevention, and that the pet’s environment has been treated for fleas. All other in contact pets, or pets in the same household, must also be put on a regular flea prevention programme as this will help to minimise exposure.