Help! My Dog Is Allergic to Fleas

Chances are that as a dog owner you are at least aware of what a nuisance fleas can be for dogs. Perhaps your own pup has been lucky enough not to have an allergic reaction to fleas, but it is a condition that can emerge at any time. And although it may appear sudden to you, the symptoms of a dog allergic to fleas can actually build over time and will be quite uncomfortable for your pup.

A flea infestation can cause great physical and emotional distress for your beloved canine companion and is only exacerbated if the dog turns out to be allergic. Unfortunately, there is no simple solution to creating a home that is flea and allergen free. You can clean and vacuum all you’d like, but the fleas may still find a way to stay.

This post is going to help you if your dog is allergic to fleas, and discuss how this happens, what symptoms to look for, and what you can do to help treat your pet from this allergic nuisance. Rest assured you and your dog can resume a healthy happy life once you are able to manage your dog’s symptoms.

But first, how does your dog develop a flea allergy in the first place?

How do Dogs Get Fleas?

It’s hard to determine how exactly a dog gets fleas, but essentially they will come into contact with the pests and the fleas will take residence in your pup’s fur. A dog can encounter fleas somewhere in his environment, or through contact with another dog who has fleas. Contact with an infected dog is thought to be the most common source.

If you are concerned that your dog has an allergy to fleas, you shouldn’t be, because it is actually the most common skin conditions in dogs. Flea bite hypersensitivity and flea canine allergic dermatitis are allergies that generally develop while the dog is young, somewhere between six months and five years of age. However, a dog can develop a flea allergy at any time during his life.

The dog generally collects an adult flea or fleas that can and will bite the dog, but the real problem is if the fleas lay eggs. These eggs will turn to larva and then a pupa. Once the adult flea is able to lay eggs on the dog it will fall off, and the eggs will mutate into mature fleas. Until the dog is treated, this life cycle will continue, and your dog will have a real infestation of fleas on his body.

Causes of Flea Allergies in Dogs

Flea allergy dermatitis is caused when a dog becomes hypersensitive to the bites of a flea. Cats also develop feline allergic dermatitis, which is most prevalent in the summer for both species. However, flea infestation may persist throughout the year, especially in warmer climates. Even in northern regions, dogs spending more time indoors in warm homes can create an environment where the fleas will continue to fester throughout the colder months.

However, any kind of temperature extremes can prohibit fleas from continuing their life cycles and becoming a year-round issue. Low humidity also helps produce a poor environment for flea growth.

Regardless of climate, hypersensitivity to the bite of a flea is the most common dermatological symptom found in dogs. As for what exactly in the flea’s bite causes the allergic reactions, the flea’s saliva seems to be the main culprit.

Fleas will inject their saliva into dogs when they bite. The flea saliva contains histamine-like compounds, polypeptides, amino acids, and enzymes that will range in size and induce a reaction. When dogs are intermittently exposed to flea bites, they may have immediate reactions that appear in as little as 15 minutes. Others may have delayed reactions that will not manifest for 24 to 48 hours.

When dogs are continuously exposed to flea bites, they will have low levels of antibodies circulating and either will not develop skin reactions or will develop them later to a much lesser degree. These dogs seem to build up a natural immune response, or a tolerance, to flea bites.

However, others may not build up these antibodies or be overwhelmed by a large infestation of fleas. When this occurs, the histamine-like compounds and other features will overwhelm the dog’s system, and an allergic reaction will occur. This allergic reaction can appear in several different ways.

Signs & Symptoms of a Flea Allergy in Dogs

The most common telltale symptom of a flea allergy is the signature severe itchy skin in dogs, a condition that is medically known as pruritis. It only takes as little as a couple flea bites a week to cause pruritis, especially if your dog has a more severe allergy.

Because a reaction can surface after just a few bites, symptoms may seem to persist even after some treatment has begun. Complicating matters further is the fact that symptoms are typically episodic, which may lead owners to believe their treatment isn’t working. However, it may just take some time to eradicate the problem.

The itching and other symptoms of flea allergic dermatitis may worsen as a dog gets older, and can even cause some secondary health issues and behavioral problems due to the dog’s hypersensitivity.

Beyond the severe itching and scratching that most often point to a flea allergy, you may also notice some hair loss or scabs on the dog’s skin due to the incessant scratching and clawing. The hindquarters are often affected more than the dog’s front or head, but lesions and flea bites can occur anywhere on the dog’s body, including its flanks, back, neck, and ears. Fleas and flea dirt may also be impossible to see by the naked human eye.

The duration and level of signs associated with a flea allergy will depend on the dog’s frequency of flea exposure, as well as the presence of any other skin condition. The degree of hypersensitivity will also vary from dog to dog.

It’s worth noting that even dogs who are not allergic to flea bites will still be annoyed by their bites, and may scratch away if they have even a few fleas. However, when a dog is allergic, these symptoms will be much more intense.

Dogs with a flea allergy and infestation will do anything they can to get at their itchy skin. They will rub against furniture and the ground, scratch, rub, lick, and even chew at what they can reach. This frequent scratching and biting can cause secondary lesions to occur, and even create areas of baldness, scaling, broken papules, traumatic moist dermatitis (hot spots), and bleeding. The dog will then become susceptible to developing secondary bacterial and yeast infections in these problem skin areas.

How is a Flea Allergy in Dogs Diagnosed?

Several factors will come into play when determining the source of your dog’s allergic reaction. However, since a flea allergy is the most common cause of skin irritation in dogs, it will often be the first thing that your veterinarian will test for.

A simple cursory physical examination can be conducted by using a flea comb to inspect your dog’s hair. These tiny combs can expose the fleas and flea dirt that may be causing your dog’s irritation. Further skin tests for mites and bacterial skin diseases may be conducted if no fleas are found. But typically, fleas are found simply by looking for them with the special comb.

It can also help to rule out other potential causes of an allergic reaction and dermatological condition. If the onset of symptoms is during the summer, it may point to a flea infestation, but it could also point to a canine allergy to another environmental trigger such as pollen.  Other conditions such as canine food allergies or medication hypersensitivity can also be a trigger for similar itching symptoms, so you will need to give a complete history of your dog’s condition to help determine when and how it started.

Using the flea comb can reveal the fleas themselves as well as excrement and larvae. Excrement will appear reddish-black and round, almost pellet or comma-shaped. And when crushed with a damp paper towel, the excrement will dissolve and produce a reddish-brown color. Those dogs that are extremely hypersensitive to the flea may appear to be free of the pests because of how excessively they groom themselves. In these cases, it may be difficult to find evidence of fleas, which will make a proper diagnosis more difficult as well.

How is a Flea Allergy in Dogs Treated?

It is essential to treat your dog’s flea allergy as soon as possible before the lesions cause a bigger problem. Fortunately, there are many options available to kill the fleas that are living on the dog’s skin. These topical treatments may include shampoos and sprays that should be used either all over the dog’s body or to specifically targeted areas. These treatments can be repeated to control the flea problem.

Flea shampoos, in particular, can be beneficial for long-term treatment and symptom relief. There are also oral medications that can help with histamine levels and provide further symptom relief as well.

One issue with the treatment of fleas is that dogs typically spend a good amount of time outdoors. They may continuously come in contact with fleas and bring them back into your home. This means you should also attempt to treat your dog’s environment as well as the dog itself. If your house or yard has a flea infestation, you may have to use insecticides to treat the pest problem.

This is especially true if you have a large yard that is populated by wildlife, if there are ever feral cats and dogs nearby, or if your dog often comes into contact with other animals at the dog park or elsewhere. These environments may bring your dog in constant contact with fleas, making continuous treatment and care your best course of action.

You should also go through your home and wash your pet’s bedding and blankets, shampoo carpets, and rugs, thoroughly clean your pet carriers, leashes and harnesses, and clean and vacuum your house thoroughly. You may even want to give your car a deep wash inside and out if you often take your dog for rides.

All of this creates a cleaner environment and improves your chances of completely getting rid of your dog’s flea problem.

Unfortunately, flea treatments will not always kill all newly acquired fleas immediately. They also will not completely repel them and keep the dog from acquiring new fleas. This is why repeated treatments will be required to continuously combat the infestation and completely eradicate the problem. This period may last up to eight weeks until the infestation can be completely eliminated.

Managing Your Dog’s Flea Allergy

Unfortunately, your dog’s flea allergy won’t go away, so you may need to repeat the above steps frequently during your dog’s entire life to keep a flea-free environment. Of course, this is a best practice regardless of whether or not your dog has an allergy to fleas, but especially if they are hypersensitive to bites.

Frequent bathing, regular application of flea treatments, and continuous cleaning of your home and outdoor environment can help keep the flea problem at bay.


Having a dog with a flea allergy can be a nuisance, especially if the problem appears to be a more recurring issue than it should be. But with a keen eye and careful attention, you can help reduce your dog’s symptoms and the likelihood of developing a full-on flea infestation. To do all you can to improve the situation, keep your dog in a clean environment and regularly do what you can to treat your dog’s surrounding. This will help to make life easier for both you and your beloved pet.



Pagán, Camille Noe. “When Your Pet Has a Flea Allergy.” WebMD, Accessed 5 Dec 2018.

“Vet Advice: Dog Flea Allergy and What to Do About It.” The Bark, 27 Mar. 2017, Accessed 5 Dec 2018.

“Flea Control and Flea Bite Allergies in Dogs.” PetMD, Accessed 5 Dec 2018.

“Flea Allergy Dermatitis – Integumentary System.” Merck Veterinary Manual, Accessed 5 Dec 2018.


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