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A Guide To Flea Allergic Dermatitis (FAD)

Aimee Labbate
  • Aimee Labbate

  • RCVS: 700039


What is flea allergic dermatitis (FAD)?

Flea allergic dermatitis (FAD) is the most common allergic skin disease in dogs and cats and is caused by allergy to proteins in the flea saliva. For affected animals, flea bites cause intense itching and inflammation in the skin, leading to overgrooming, licking, biting and scratching at the skin, which in turn causes further damage and often results in skin infection.

What are the symptoms of flea allergic dermatitis (FAD) in dogs & cats?


  • Licking, chewing, scratching
  • Inflamed skin and hair loss typically along the lower back and rump
  • Spots on the skin with crusts and scabs
  • With time the skin can become thickened and pigmented (dark)

Cats (tend to show more variable signs that may include):

  • Overgrooming (this tends to be much less obvious in cats as they often do it in secret!)
  • Generalised dermatitis (small spots and scabs) that can affect the whole body, or be more localised on the lower back
  • Alopecia on the lower back or tummy (due to overgrooming)
  • Raised, red nodules or ulcers on the skin, lips or inside the mouth (eosinophilic granuloma complex)

How is FAD diagnosed in dogs & cats?

FAD is normally diagnosed based on the clinical signs above and the presence of fleas. You can check for fleas using a flea comb or by doing the ‘wet paper test’. This involves combing the animal’s coat onto a piece of wetted paper – flea faeces (that contain blood) will leave a red/brown streak as the blood leaches out.

There are more sophisticated skin and blood tests that can be performed if the wet paper test was negative, but often the best way to diagnose FAD is to simply treat for fleas and monitor the response.

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How is FAD treated in dogs & cats?

Rigorous flea control and prevention is crucial for the management of FAD in dogs and cats. This involves treating the pet and all other animals within the household with an anti-flea product on a regular basis – these are usually in the form of a spot-on or oral tablet.

Given that just one or two flea bites can trigger the condition, it is vital that you stay up to date with their flea treatment. At PocketVet we offer a monthly subscription for flea control, so that the treatment automatically arrives through your letterbox without you having to think about it, meaning you never fall behind with your pet’s flea treatment. Please follow this link to find out more.

Surprisingly, 95% of the flea population is in the environment (your sofas and carpets!) rather than on the animal. It is therefore crucial that you also treat the environment to prevent your animal from continually being reinfested. This is best done through a combination of the following:

  • An environmental flea spray such as Indorex (which is available here in our shop). This only needs to be used every 6-12 months but please follow the directions on the can.
  • Regular vacuuming as this helps to remove fleas and their eggs from the carpet and soft furnishings. It also helps to stimulate fleas to emerge from their pupae, where they will then be killed by contact with the spray in the environment.
  • Washing of pet’s bedding and human bedding that the pet uses.

For animals that are very severely infected, your vet may suggest using corticosteroids for a short period to control the itching while flea control is implemented. Steroids have many side effects, so they are not recommended for long-term use if possible.

Sometimes antibiotics may be prescribed where a skin infection is present (usually as a result of self-trauma to the skin).

Omega-fatty acid supplements can also be beneficial in helping to control FAD and allergic skin disease in general, by helping to improve the skin barrier function. Again, these are available to purchase in our shop.

What is the prognosis of FAD in dogs & cats?

If your pet suffers from FAD then they will remain allergic for life, so rigorous flea control is key. Thankfully, many products are now available and so this is relatively straightforward and inexpensive. Please talk to one of our vets about a treatment plan for your pet.

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