Flea bite hypersensitivity

Flea bite hypersensitivity is an allergic reaction caused by exposure to flea saliva. When fleas bite and feed on dogs or cats, their saliva can cause an allergic reaction in the skin.

Signs of trouble

In many cases, dogs and cats with flea bite hypersensitivity will bite the base of their tail and scratch frequently. Many dogs experience characteristic hair loss or thinning hair above the tail base that may become more generalized and extend to the inside of the thighs, or abdomen. Dogs may occasionally develop secondary skin infections and other skin lesions. Cats may develop small circular crusts at the base of the neck or base of the tail and/or red raised areas on their skin.


Diagnosis is based on patient history, physical examination, skin testing with flea antigen, and response to treatment. The presence of fleas or flea dirt along with the characteristic pattern of hair loss is also a helpful finding. The absence of fleas does not rule out a diagnosis because some sensitive animals may require only periodic flea exposure to develop skin problems. Your veterinarian may need to perform additional diagnostic tests to rule out other secondary skin issues caused by flea exposure and the allergic reaction they caused.

Treatment and prevention

Since fleas cause the hypersensitivity, flea control is essential. Even if you no longer see fleas, you should continue use of the year-round flea control product because immature flea stages may be lurking in your environment. Medication may also be provided to help treat the skin irritation associated with flea bite hypersensitivity and make your pet more comfortable.

The importance of prevention

The best way to protect your pet from fleas is prevention. Many of these products are easy to administer and need to be given only once a month year-round, making it convenient for today’s busy pet owner.

Brought to you as a service by Bayer Animal Health
© 2006 Bayer HealthCare LLC, Animal Health Division,
Shawnee Mission, Kansas 66201.