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Flea-Bite Hypersensitivity and Flea Control


•  “Hypersensitivity” is an increased sensitivity or reaction in the skin due to the presence of a foreign substance; in flea-bite hypersensitivity, the foreign substance is found in flea saliva; the reaction is immune based and would be considered to be an “allergic” reaction
•  “Dermatitis” is the medical term for inflammation of the skin
•  “Antigens” are substances that induce sensitivity or immune response
•  “Flea-bite hypersensitivity”—hypersensitivity or allergic reaction to antigens in flea saliva, with or without evidence of fleas and flea dirt
•  “Flea infestation”—fleas and flea dirt are present on the pet, with or without signs of flea-allergy dermatitis
•  “Flea-bite dermatitis”—inflammation of the skin due to the flea bite itself; it is not an allergic or hypersensitivity reaction, but rather an irritant response to flea bites


•  Flea-bite hypersensitivity—unknown inheritance pattern; more common in breeds with atopy (disease in which the pet is sensitized [or “allergic”] to substances found in the environment [such as pollen] that normally would not cause any health problems)

Signalment/Description of Pet


•  Dogs
•  Cats

Mean Age and Range

•  Flea-bite hypersensitivity—rare in pets less than 6 months of age; average age range, 3–6 years, but may be seen at any age

Signs/Observed Changes in the Pet

•  Determined by the severity of the reaction and the degree of exposure to fleas (that is, seasonal or year-round)
•  Itchiness (known as “pruritus”)
•  Compulsive biting
•  Chewing (“corncob nibbling”)
•  Licking, primarily in the back half of the body, but may include other areas
•  Signs of fleas and flea dirt; finding fleas and flea dirt is beneficial, although not essential, for the diagnosis of flea-bite hypersensitivity
•  Sensitive pets require a low exposure to fleas to have an immune response and they tend to over groom, removing evidence of flea infestation, and making identification of parasites difficult
•  Hair loss (known as “alopecia”)
•  Small, raised skin lesions (known as “papules”)
•  Darkened skin (known as “hyperpigmentation”) in dogs
•  Thickening and hardening of the skin, usually associated with hyperpigmentation (known as “lichenification”) in dogs
•  “Hot spots” in dogs
•  Miliary dermatitis (skin inflammation characterized by numerous, small, crusty bumps) in cats


•  Fleas
•  Immune response to flea saliva (flea-bite hypersensitivity or flea-allergy dermatitis)

Risk Factors

•  Flea-bite hypersensitivity—intermittent exposure to fleas increases likelihood of development; commonly seen in conjunction with atopy (disease in which the pet is sensitized [or “allergic”] to substances found in the environment [such as pollen] that normally would not cause any health problems)


Health Care

•  Outpatient treatment

Follow-Up Care

Patient Monitoring

•  Itchiness (pruritus)—a decrease in itchiness indicates the flea infestation and/or flea-bite hypersensitivity is being controlled
•  Fleas and flea dirt—absence is not always a reliable indicator of successful treatment in very sensitive pets

Preventions and Avoidance

•  Year-round warm climates—year-round flea control is required
•  Seasonally warm climates—begin flea control in May or June, as directed by your pet’s veterinarian

Possible Complications

•  Secondary bacterial infections
•  Sudden (acute) moist dermatitis, also known as “hot spots”
•  Acral lick dermatitis (inflammation of the skin characterized by a firm, ulcerated lesion on a leg, caused by constant licking)

Expected Course and Prognosis

•  Prognosis is good, if strict flea control is instituted

Key Points

•  Flea control is important for dogs and cats
•  No cure exists for flea-bite hypersensitivity
•  Flea-allergic pets often become more sensitive to flea bites as they age
•  Controlling exposure to fleas is currently the only means of controlling signs; “allergy shots” (known as “hyposensitization”) for flea-bite hypersensitivity are not effective


Blackwell’s Five-Minute Veterinary Consult: Canine and Feline, Fifth Edition, Larry P. Tilley and Francis W.K. Smith, Jr. © 2011 John Wiley & Sons, Inc.