Educational Resources

Flea Allergy Dermatitis

Flea allergy dermatitis (FAD) is the most common allergy that affects cats. It occurs when a cat develops hypersensitivity to proteins (allergens) in flea saliva, which is injected into the cat’s skin during a flea bite. It only takes one flea bite to trigger an allergic reaction!

Clinical Signs

  • Itchiness, or pruritus, especially around the head/neck and tail region
  • Hair loss, especially around the tail or flank region
  • Numerous small scabs all over the body (miliary dermatitis) or larger areas of skin irritation (eosinophilic granulomas)
  • Clinical signs will vary depending on the severity of the allergy


  • Often the diagnosis is made upon visualization of fleas and/or flea dirt in combination with the clinical signs above.
  • Presumptive diagnosis is sometimes made if there is a history of flea exposure.
  • If few fleas are present or a visual diagnosis cannot be made, a blood allergy test or intradermal skin test may be required.


  • Preventing flea bites THROUGH STRICT FLEA CONTROL is the most essential aspect of therapy!
  • Flea treatments that contain medications that kill both the adult and the immature stages of the flea are recommended. Applications may need to be more frequent than with non-allergic cats; your veterinarian can determine this.
  • Environmental treatment for fleas is recommended—see Flea Control for Cats
  • Depending on the severity of the allergy, your veterinarian may make several therapeutic recommendations.
    • Antihistamines or Prednisolone (or other steroids)—These medications reduce inflammation of the skin by blocking the production of inflammatory substances within the body.
    • Allergy shots—Small amounts of proteins from flea saliva (antigens) that stimulate the allergic response are injected into the body so that the immune system will develop tolerance to the allergens. This requires either blood or skin allergy testing.

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