Ask The Doctor – A Case of Flea-Allergic Dermatitis in Cats


A raw spot on my cat’s body
Q Recently, I noticed that my seven-year-old male cat, Bisco, was excessively grooming his hindquarters. When I investigated the site, I discovered a raw red spot where Bisco had licked the fur and skin off. The vet explained that Bisco had developed a “hotspot” and that these were fairly common in cats, particularly during the summer.

Fortunately, Bisco responded well to a shot of antibiotic and treatment with prednisolone, but I am wondering how common this condition is in cats — I have heard about it frequently in dogs — and that perhaps other Catnip readers would be interested.
Roberta Klein

A Dear Roberta: You are describing a very common problem: excessive grooming/licking over the hindquarters during summer and fall months. This is most likely caused by flea-allergic dermatitis (FAD) and it is the most common skin problem impacting cats.

Flea allergy dermatitis is actually different than just having fleas. As an analogy, it is painful for me if I am out in the yard and am stung by a bee. But some people have a more severe reaction, and when stung, they need to go to a hospital. These people are allergic to bee stings.

Somewhat similarly, cats may be allergic to fleas. When a flea bites, it injects saliva into the cat’s skin and the allergic response is to the flea saliva. A single injection of saliva (a single bite) can make an allergic cat itch for up to two weeks! This is different than just having fleas. Only those cats with allergic responses experience the severe itching response. Typically, FAD cats itch over the hindquarters. Some also experience itching down their hind legs, in the groin and along their spine.

The best treatment for FAD is to eliminate fleas. As well, a short course of anti-allergic medicine (prednisolone) is needed to stop the itch. To avoid the problem in the future: An owner should prevent fleas. Your veterinarian can recommend an appropriate product that is best for your cat.
Michael Stone, DVM, DACVIM
Clinical Assistant Professor
Cummings School of Veterinary
Medicine at Tufts University


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