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A Veterinarian Answers FAQs About Flea Allergy Dermatitis in Dogs

Updated on August 15, 2017
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Donna partners with Dr. Cathy Alinovi, a retired veterinarian, to create informative pet health articles.

Before you get a dog or cat, you might as well accept the fact that at some point, you will have to deal with a flea issue with your fur child.

While getting rid of the occasional flea is a minor inconvenience for pet and owner, for those dogs with a propensity for flea allergy dermatitis (FAD), fleas can be a major health risk. Dr. Cathy Alinovi of Hoofstock Vet shares expert advice on how pet parents can protect their pet’s health and well-being.

Dr. Alinovi discusses the symptoms, treatment and prevention of flea allergy dermatitis in dogs.
Dr. Alinovi discusses the symptoms, treatment and prevention of flea allergy dermatitis in dogs. | Source

What's the Problem?

What is flea allergy dermatitis (FAD)?

Dr. Cathy: FAD is an allergic reaction to flea saliva. Fleas bite dogs, injecting their saliva into the dog’s skin so the blood does not clot, and drink the blood. Dogs with FAD are allergic to the proteins in the flea spit.

Within 15 minutes to 24 hours of a flea bite, the allergic dog reacts to the saliva. The reaction causes an itch, which causes the dog to chew. This leads to self-mutilation because the itch won’t stop.

Soon, the skin is damaged and the natural barrier no longer defends against bacteria. The result is a skin infection. The crazy part is it only takes one fleabite to make this happen.

What is the difference between FAD and fleabites?

Dr. Cathy: Fleabites are just a nuisance for non-allergic dogs. FAD is a hypersensitivity reaction that makes the body inflamed. It takes one fleabite for the whole body to blow up.

What percentages of dogs does FAD affect?

Dr. Cathy: Approximately 10% of dogs have flea allergy; it is the most common skin condition in dogs. Sixty-one percent of dogs between one to three years of age are diagnosed with FAD.

If it is not diagnosed and treated promptly, is FAD dangerous?

Dr. Cathy: Because itchy dogs chew, and chew, and chew, they make their skin raw. The endless chewing breaks blood vessels in the skin, causing damage to the skin and the local immunity; the result is a skin infection.

Your vet can determine if your dog has a flea allergy.
Your vet can determine if your dog has a flea allergy. | Source

Symptoms and Diagnosis of FAD

DC: What symptoms do dogs with FAD exhibit?

Dr. Cathy: Itching, chewing, digging, head shaking, which are all the things that drive pet parents crazy and keep both dogs and people awake at night! Other signs include shedding, bald skin, hot spots, skin infection (usually a combination of bacteria and yeast), crusty skin, dark pigmented skin, and an odor.

DC: How do you diagnose FAD?

Dr. Cathy: Diagnosis is by elimination, so you eliminate the fleas. If the allergy goes away – you have a magical diagnosis of FAD. FAD can also be diagnosed by a blood test, as the blood test will detect high levels of antibodies to flea saliva.

Flea Problems?

How a big a problem are fleas for your fur children?

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Traditional Treatment Options

What treatments do you recommend for FAD?

Dr. Cathy: Get rid of the critters! This means flea protection. There are many methods ranging from all-natural options to chemicals. What you chose depends on how bad the problem is and how much risk you are willing to take.

Eliminate the Fleas

My typical advice in the office is to use a monthly flea preventative, and then go home and vacuum the house as if you are doing a major spring-cleaning. Vacuum the corners, nooks, and crannies; get in, under and around furniture; wash all the dog and cat beds, pillows and sleeping areas; then take the vacuum bag outside as soon as you are done so fleas don’t crawl out of the bag and re-infest the house. Repeat in two to three weeks to match the flea life cycle (see below).

Flea Preventatives

What to use? Most flea preventatives are chemicals, and I have seen reactions to everything out there. There are topical spot-ons that are essential oil-based, some others use generally safe chemicals, and yet others use harsh chemicals that frequently result in problems.

My rule-of-thumb is to use something a vet would carry, for the safety of your pet. There are chewable tablets that have come out in the last 1 to 2 years that control fleas for 30 days. You can use diatomaceous earth on your dog and/or in the yard. Finally, there are also some garden insect control products—but read the label carefully—these can be toxic.

Relieving FAD

As to treating the symptoms of flea allergy? We have to soothe the skin. By the time there is a hot spot—once the skin is red, bloody and oozing—there is infection. Most commonly, this is treated with antibiotics, either topical or oral, as the infection can be rather deep in the skin layer. Many dogs need something to relieve the itch.

Frequently, antihistamines, like Benadryl, are not enough to break the itchy cycle; often, it takes steroids to stop it. Steroids are a strong medication with potential to harm the body, especially after long-term, repeated use.

If I have to use steroids, I try to use them once to give the family relief, and then discover the underlying cause and prevent any future problems. Some vets prescribe medicated shampoo; you can also use shampoos with tea tree oil or lavender to clean/disinfect the skin.

It takes rigorous house cleaning to get rid of flea infestations.
It takes rigorous house cleaning to get rid of flea infestations. | Source

Natural Alternatives

Are there any natural remedies (such as borax) that will give rid of flea infestations in homes?

Dr. Cathy: Flea infestations are less common in homes without carpet. Wall-to-wall carpet can hide flea eggs and larvae so homes with carpeting may need more help than simply vacuuming.

While “natural,” borax is still harsh. If you use borax to get rid of fleas, wear gloves, work it deep into the carpet, allow to sit for 24 hours, vacuum the heck out of it, and then you can let pets and kids back on the carpet. There is a less toxic product—sodium polyborate powder—but it’s only less toxic than borax. Always be careful when treating the environment. Other natural remedies include:

  1. Food grade diatomaceous earth can be put on the carpet and left there, but be sure to work it in. Diatomaceous earth dries out fleas, so after you vacuum, put down more for more flea drying.
  2. Cedar oil can be applied to your dog, or its bed, but I would not suggest that you use it directly on the carpet.


The bite from just one flea can be enough to cause flea allergy dermatitis.
The bite from just one flea can be enough to cause flea allergy dermatitis. | Source

Keeping Fleas at Bay

How can owners prevent future outbreaks of FAD?

Dr. Cathy: Continue flea prevention measures. Many holistic vets advocate using a flea comb. While flea combs are awesome at finding and catching fleas; just remember, if your dog has FAD, all it takes is one flea to start the horrible cycle all over again.

For these pets, I recommend monthly flea prevention in the form of either essential oil or chemical. There are also some essential oil based products that must be reapplied every three to four days. They work great and are less toxic; the pet parent just has to keep up with frequent applications.

Life Cycle Stages

  1. Adult fleas lay eggs, which hatch in a few days and turn into larvae.
  2. The larvae eat flea “dirt” and go through three developmental stages before turning into pupae after a week or so.
  3. Pupae hang out in their cocoon for up to a week then hatch to blood-sucking adults.

Flea Life Cycle

What is the life cycle of a flea?

Dr. Cathy: Why should you care? Primarily, because if you know when the next batch of nasty critters will hatch, you can be armed to kill them before they re-infest your home or bite your poor flea allergic dog.

The flea life cycle can be as fast as two weeks, while the typical length is four to six weeks, but it can be as long as two years.

Therefore, it can take as little as two weeks for the next batch of critters to re-infest. That’s why I recommend repeating “spring cleaning” every two weeks for two months to take care of an infestation problem.

Fun Facts Worth Knowing

Did you know:

  • Fleas transmit tapeworms – eat a flea, get a tapeworm.
  • Only one percent of the total flea population is adult; that means if you see 10 fleas, there are 90 hidden eggs, pupae and larvae ready to become adults in less than two weeks!
  • The pupae is the stage that can stay dormant for months to years. Once stimulated – boom, seven days until all heck breaks loose.
  • Flea “dirt” is really digested blood from the larvae feeding on its prey.


It’s easier to prevent an infestation than eliminate it.

Following good sanitation practices and keeping pet bedding cleaned and sanitized is a good first step, but you should examine your dog regularly for signs of fleas, ticks or other pests.

For instance, when you bathe or groom your pet, run your hands gently over the entire body.

If you feel a bump or irregularity in the skin, it’s probably a good idea to have your family vet check out your pet to determine what might be causing the problem. Prevention trumps cures, and is less stressful for both you and your best friend.


This veterinary medical information is based on information provided during a telephone interview with a professional, qualified, retired veterinarian. However, it is provided for educational purposes only. It is not intended to replace the advice of your own veterinarian. Always seek your veterinarian’s advice about your pet’s health.

While this information is periodically researched and updated (under the guidance of veterinary input) in the attempt to be timely and factual, no guarantee is given the information is correct, complete, and/or up-to-date.

Recommendations as to therapeutics, diagnostics and best standards of practice in the veterinary industry and/or opinions between professionals may differ or change as technologies and information changes. You should not use this article as your sole source of information on any matter of veterinary health or attempt to self-diagnose or treat your pets as the information herein may not be appropriate for your pet. The safest option for you and your pet is to rely on the advice of your veterinarian to diagnose and recommend the best treatment options.


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