flea dermatitis causes and treatment

Flea Dermatitis: Causes & Treatment

Fleas are everywhere. These pests have been around for millions of years. Despite advances in pesticide technology and our understanding of their life cycle as well as how to fight them, they still manage to pester our dogs and cats, leaving behind a very characteristic skin condition we now know as flea allergy dermatitis, or simply flea dermatitis. This skin condition can bring a lot of discomfort to our beloved pets especially dogs that seem like natural magnets for the critters. Understanding how it occurs and what causes it can help us find more meaningful solutions to flea dermatitis.

What Causes Flea Dermatitis?

Most experts agree that flea dermatitis is a kind of allergic reaction brought about by the introduction of proteinaceous molecules into the different tissues of the pet’s skin.

According to the MSD Veterinary Manual, flea allergy dermatitis develops when fleas bite the skin of our dogs to feed. These flightless insects inject their saliva that is filled with a variety of compounds that mimic the action of histamine, a natural pro-inflammatory substance. Other molecules that may be present in the saliva of fleas include amino acids and polypeptides. It is this combination of protein-based molecules and histamine that leads to the initiation of Type I and Type IV hypersensitivity reactions.

Type I hypersensitivity reactions involve the release of pro-inflammatory substances like histamine from basophils and mast cells. This type of reaction is mediated by Immunoglobulin-E and is typically described as immediate or almost instantaneous. On the other hand Type IV hypersensitivity is the direct opposite of Type I reactions. If Type I reactions are super-fast, Type IV reactions are delayed. This type of reaction involves the activation of helper T-lymphocytes which, in turn, activate a variety of other cells to initiate an immune response.

As such, there are dogs that can react almost immediately to a flea bite, causing an inflammatory reaction within 15 minutes of the bite. Others have delayed reaction, often requiring 24 to 48 hours before any sign of skin inflammation becomes visible. In some cases, both immediate- and delayed-onset hypersensitivity reactions can occur.

Experts say that dogs that are continuously exposed to flea bites can develop immunologic tolerance. This means that they still have hypersensitivity reactions, but the skin condition is not that severe.

Flea dermatitis also occurs in cats, albeit infrequently. The mechanism of disease-causation is also not understood clearly.

How Do I Know If My Pet Has Flea Dermatitis?

Different dogs will react differently to the bite of fleas. Some may not even show allergic dermatitis at all. This depends on a host of factors such as the frequency of exposure to fleas, degree of hypersensitivity, duration of the disease, the presence of concurrent or secondary skin condition, and the effects of current or previous treatments. Typically, a dog that manifests any of the following symptoms can be expected to have flea dermatitis:

  • Itching which can be mild to severe
  • Presence of lesions that are raised and crusting typically found on the dog’s lower back, inner things, tail head, and back of the thighs
  • Scratching, chewing, licking, nibbling, or even rubbing of the sides of the body, the ears, neck, lower back, and backside
  • Brownish stain on the dog’s hair
  • Hair loss and skin redness in affected area
  • Hyperpigmentation in affected area
  • Presence of papules and scaling as well as lesions with reddish brown crusts in affected areas

For dogs with severe flea dermatitis, they can present with the following manifestations.

  • Hair loss affecting almost the entire body of the dog
  • Severe redness
  • Self-inflicted trauma or skin injuries
  • Hot spots or traumatic moist dermatitis
  • Severe seborrheic dermatitis
  • Severe hyperpigmentation of the skin
  • Increased thickening of the dog’s skin

How Is Flea Dermatitis Diagnosed?

Aside from the classic manifestations that are typically attributed to this kind of skin condition, veterinarians have several other ways of establishing a more definitive diagnosis.

For example, the timing of the dermatitis is usually around late summer which coincides with the peak in flea populations. The age of the dog can also help distinguish flea dermatitis from other skin problems since this condition rarely develops in puppies below the age of 1 year.

One way to aid in the diagnosis is if the presence of fleas can be established. Flea excrements that are shaped like a comma, pellet, or cylinder and have a reddish black color can often indicate the presence of adult fleas. Unfortunately, if the dog is hypersensitive to fleas, you may not actually see any flea or excrement on its skin because of self-grooming behavior that has become excessive.

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Aiding in the diagnosis is intradermal skin testing. A substance is injected under the dog’s skin and observed over a period of time. If the wheal produced by the injection grew by about 3 to 5 millimeters within 15 to 20 minutes, then your dog is positive for a Type I hypersensitivity reaction. If there is no increase in the wheal size within this time frame, diagnosis is deferred for another 24 hours to allow for the determination of a Type IV reaction. Sadly, this test doesn’t conclusively rule out the presence of flea dermatitis. It only shows that your dog is allergic to the antigen.

A more definitive diagnostic test involves the use of blood tests directed at identifying the presence of IgE immunoglobulins.

Like all diseases, your vet will have to make sure that your dog has flea dermatitis and not food allergy, bacterial folliculitis, atopic dermatitis, demodectic or sarcoptic mange, and other skin conditions brought about by other ectoparasites.

How Is It Treated?

Treating flea dermatitis is not a one-off thing. You cannot expect results with a single treatment session alone. Veterinarians always recommend a very comprehensive approach to the treatment of flea dermatitis.

There are three principal goals of flea dermatitis treatment. They include the following.

  1. Management of symptoms
  2. Elimination of causative factors
  3. Management of irritants

Your veterinarian may provide a host of medications to relieve the intense itching that your dog experiences. For this, he may prescribe an appropriate antihistamine or other medications that work well to control the intense itching in dogs. The inflammation also needs to be reduced. Anti-inflammatory medications can be prescribed. If there are secondary infections, the appropriate antibiotics or even antifungals may be ordered.

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The removal of fleas on your pet’s skin helps to break the cycle especially when symptomatic treatment has already been initiated. What this means is that you need to remove the fleas from your dog while it is undergoing treatment for its itching, inflammation, secondary infections, or any other accompanying symptom. Your vet may recommend a flea treatment for dogs that don’t have any adverse interactions with the drugs used for symptomatic management. If none is available, you will need to manually remove fleas, flea eggs, and excrements from your dog’s skin using a dog flea comb with a rating of about 32 teeth per inch. If you have other pets in the home you may also want to start treating them with flea medications or with a flea collar.

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Avoiding skin irritants is the third goal of flea dermatitis management. Your dog doesn’t need additional insults to its already-compromised skin integrity. If you need to use topical flea products on your dog, make sure to talk with your vet first as these may contain ingredients that may further irritate your dog’s skin. For instance, many flea shampoos as well as sprays can actually contain chemicals like alcohol that can produce rash or worsen wounds.

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Are There Natural Remedies for Flea Dermatitis?

We mentioned above that one of the critical aspects of flea dermatitis treatment is the avoidance of additional skin irritants. As such, while natural remedies have been proven by many pet parents to be effective in alleviating the symptoms of such conditions in their dogs, we still would like to caution you when using these remedies. Always seek the advice of your vet.

Some of the natural remedies that pet parents use in the management of flea dermatitis include herbal remedies such as rosemary, yellow dock, eucalyptus, and fennel which can be mixed in equal parts before sprinkling onto your dog’s coat. They don’t actually manage the symptoms but are great flea repellents. Some also advise the use of witch hazel which can help reduce inflammation and minimize the severity of itching. While these methods have been used by many pet parents, you should still consult with your veterinarian if it is okay to use such preparations on your dog.

Perhaps one of if not the most important natural remedies for flea dermatitis is the observance of proper pet grooming. Using flea comb to remove these pests from your dog can help break the vicious cycle and prepare your pet for complete healing. Proper nutrition is also important as it provides the necessary ingredients for stronger and healthier immune system while contributing to optimum coat and skin health.

Flea dermatitis may look like any other skin problem in dogs and cats. However, this can cause a lot of discomfort as well as expose your dog to the risk of developing secondary infections. Knowing how to spot flea dermatitis and what to do about it can help you provide better care and support for your pooch.


  1. Hany M Elsheikha, Flea Allergy Dermatitis: The Continued Challenge, MAG Online Library
  2. Anna Burke, What Do Flea Bites Look Like on Dogs?, The American Kennel Club
  3. Souza, Candice, DMV, Fleas, Flea Allergy, And Flea Control: a Review, eScholarship

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Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.