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Flea Allergy in Dogs: Everything You Need to Know

How does a flea allergy differ from your dog just having fleas? For some unlucky dogs, fleas are more than just a nuisance; they actually cause a severe and uncomfortable allergic reaction in their skin! Dogs with flea allergies need their pet parents to be extra vigilant, but with the safe and effective flea prevention products that we have available today, flea allergies are completely manageable if even preventable!

How Does a Teeny Tiny Flea Cause an Allergy?

When a flea bites a dog they inject some saliva into the dog’s skin. Normally, flea saliva is harmless to the average dog, and some dogs can even be covered with fleas and not seem to be bothered much at all! However, flea saliva contains a protein that in some dogs causes a severe allergic reaction when it breaches the dog’s skin barrier. This explains why some poor flea-allergic dogs can have severe skin issues, even if they only have 1 or 2 fleas! 

Dogs with a flea allergy are extremely hypersensitive to the bite of even one single flea! Their immune system overreacts, triggering an inappropriate inflammatory response, resulting in excessive itching, nibbling, hair loss, scabs, redness, and skin infections. Yep, dogs can get allergies, and a flea allergy is the most common type! Typically, flea allergies are diagnosed in dogs between 1-5 years of age, and dogs that have environmental or food allergies can be more prone to a flea allergy as well.  

Why Don’t I See Fleas on My Dog?

So, how do dogs get fleas and how can you detect them? How could the itching, scratching, nibbling, and hair loss be related to fleas if pet parents can’t see any crawling around? Veterinarians are experts at deciphering the somewhat subtle signs that different allergies and skin conditions will leave for us. Your geographic location (warm, humid temps = flea country), patterns of itching and hair loss, thinning hair over the rump and tailhead region, and especially the lack of application of a monthly prescription-strength flea control product are some of the top clues that will lead us in the direction of a flea allergy diagnosis. Occasionally during physical exams, we are lucky enough to flea comb just the right spot to produce a flea culprit, or some “flea dirt” (black sandy looking flea poop) in order to tell if your dog has fleas. But sometimes, like you, we cannot find a single flea either! This does not mean that they are not behind the whole production though. Dogs with flea allergies are so sensitive and tormented by the bite of a single flea (sometimes even for weeks), they will immediately find that flea, nibble it off and get rid of the evidence. Sometimes they are so bothered and distraught, they will take skin and hair with it! 

Dogs with a flea allergy tend to excessively self-groom, removing all evidence of a flea infestation but leaving behind the damaged, unhealthy, and inflamed skin. Typically, specific skin allergy tests are not used to diagnose a flea allergy – your vet might perform some other skin tests to rule out different parasites and infections, but the signs and physical exam findings often speak for themselves. A positive response to flea treatment (meaning, the skin problem improves and resolves once flea prevention is applied) will also support the diagnosis of a flea allergy. 

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Does Just the Dog With the Allergy Need Flea Prevention?

If the other dogs and cats in the home seem fine … why do they need flea treatment too? The cats don’t even go outdoors!? The most effective and important aspect of controlling a flea allergy in your dog is simple: prevent fleas from gaining access! In order to completely avoid flea bites and prevent a flea infestation from procreating in the interior home environment, it is essential that all opportunities for fleas to feed and reproduce are taken away. If the flea allergic dog is the sole recipient of monthly prevention, the other unprotected animals in the home are free and available for a flea field day, including hosting female fleas who will lay 50+ flea eggs per day! Fleas see dogs and cats as gracious and welcoming hosts, and our homes as a wonderful place to raise their gigantic families … unless ALL the pets are protected monthly as recommended by our veterinarians as well as your family veterinarian!  When a flea allergy is diagnosed, your vet will detail for you how to get rid of fleas on your pup; including plans for starting all pets in the home on a prescription-strength flea prevention treatment, cleaning the home environment, and treating with medication any severe skin inflammation or infection arising from the intense itching. 

Talk to a Trusted Vet

With the wonderful, safe and effective flea prevention products on the market today, all dogs and cats in the home should be treated as directed for their own health and well-being, as well as to protect any other animals in the home–especially if they are unfortunate sufferers from a flea allergy. If you have any additional questions about your flea allergic pet, or about fleas and allergies in general, our veterinarians at AskVet are ready to chat anytime!


Written by:

Alexa Waltz, DVM

Dr. Waltz was raised near the beaches of Southern California but has spent her adult life living all over the beautiful United States while serving in the military and as a military spouse. She left California for the first time to pursue a career as a veterinarian at Louisiana State University School of Veterinary Medicine and graduated as a Doctor of Veterinary Medicine in 2006. She was accepted into the US Army Health Professionals Scholarship Program during vet school and upon graduation spent her military years as a veterinarian in San Diego working for the US Marine Corps and US Navy Military Working Dog programs as well as caring for pets of service members. After her military service, she became a civilian veterinarian and continued as a small animal general practitioner at clinics in California, Rhode Island, Colorado, and Maryland. Dr Waltz loves to see her “in person” patients just as much as communicating with and assisting pet parents virtually on AskVet. Dr Waltz is also a Mom to 3 humans, 2 guinea pigs, and 1 Australian Shepherd and in her spare time she loves traveling, adventures, exercising, and doing just about anything out in nature!




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