Flea allergy dermatitis in dogs and cats: Symptoms, treatment and prevention

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Reviewed by Dr Sylvia Shortreed BVSc

Flea allergy dermatitis (FAD) is one of the most common skin conditions found in dogs and cats. Learn how to recognise the signs of FAD, get proper treatment and most importantly, prevent it from happening in the first place.

Flea bites expose pets to flea saliva – which some pets become allergic to over time. This allergic reaction is known as flea allergy dermatitis or FAD.

FAD is an allergic skin condition that mostly affects pets aged over one year and commonly occurs in dogs and cats with underlying skin diseases like atopic dermatitis.1, 2 Pets with FAD can damage their skin by constantly scratching, biting or licking, and this damage can lead to secondary skin infections.

What does FAD look like?

The most common sign of FAD in dogs and cats is intense itchiness, but there are others to watch for:

  • Appearing restless and uncomfortable
  • Spending a lot of time grooming, chewing, biting, licking and scratching themselves or rubbing their skin against objects
  • Hair may be stained brown from licking – especially obvious in white pets
  • Skin changes in dogs: hair loss, rash, reddened or darkened skin, thickened skin, scratches or wounds from self-trauma, typically along the lower back and base of the tail, the thighs and belly
  • Skin changes in cats: hair loss and rash typically involving the back half of the body (belly and back), hind legs (inner and back surfaces), back of the neck, and less commonly on the head

It's also important to look for damage to your pet’s skin that can lead to secondary infections (reddened, moist areas called “hot spots”) that will exacerbate the itching and can be very painful.1,2

How to treat FAD in your pet

If you do suspect your dog or cat has FAD, take them to your vet – they will look for evidence of fleas and may perform a flea elimination trial, skin tests or blood tests.

Bites from just one flea can be enough to trigger intense itching in a pet with FAD, and your vet may diagnose FAD even if fleas or flea dirt (flea faeces) aren’t visible.

Minimising the number of flea bites is the most important part of managing FAD. You can control fleas year-round with an effective, fast-acting product like Advocate™Seresto™Advantix™ (dogs only)  or Advantage™, thanks to imidacloprid – the super active ingredient, which kills fleas on contact. This means that fleas don’t need to bite your pet and cause further irritation before the treatment takes effect.3 Once fleas come into contact with your pet, they are affected within 3-5 minutes. Reinfesting adult fleas are killed within 2 hours.4

Another very effective flea treatment option for your dog is Credelio™ PLUS, an oral monthly chew that starts killing fleas within 2 hours5, eliminating all fleas present on your dog in 6-12 hours with continued flea protection for a full month.

All pets in the household should be treated whether or not they show signs of flea infestation.

Talk to your vet about FAD management

As well as using a fast-acting, effective flea control to minimise flea bites, your vet may also advise the following treatments to help heal your pet’s damaged skin, eliminate bacteria and alleviate the itching:

  • Topical (applied directly to the skin) or systemic (given orally or by injection) antibiotics
  • Topical or systemic anti-inflammatories
  • Medicated shampoos and conditioners

Always consult your vet when using a medicated shampoo and/or conditioner in combination with flea-prevention products. Topical flea prevention products should be applied to a dry coat.

Always read and follow label directions.


  1. Noli, C, Foster, A and Rosenkrantz, W, Veterinary Allergy, 2013; 1st edn, Wiley Blackwell, New Jersey.
  2. Miller, WH, Griffin, CE and Campbell, KL, Muller and Kirk’s Small Animal Dermatology, 2013; 7th edn, Elsevier Mosby, Missouri.
  3. Mehlhorn, H, Hansen, O and Mencke, N, Comparative study on the effects of three insecticides (fipronil, imidacloprid, selamectin) on developmental stages of the cat flea (Ctenocephalides felis Bouche 1835): a light and electron microscopic analysis of in vivo and in vitro experiments, Parasitology Research, 2001; 87(3): 198-207.
  4. Stanneck D Parasites & Vectors 2012 102 Efficacy of an imidacloprid/flumethrin collar against fleas, ticks, mites and lice on dogs
  5. Cavalleri D et al. Parasit Vectors 2017;10:521. Elanco Data on File. Study NAH-14-242. Cavalleri D et al. Parasit Vectors 2017;10:529.

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