Does Your Dog Have a Flea Allergy?

Updated May 1, 2022
dog lying in the grass with a ball


Fleas are the most common external parasite found on dogs and cats worldwide. Flea allergy dermatitis (known as FAD) is the most common dermatologic disease in domestic dogs in the United States. A study has shown a 13% increase in FAD in dogs over the last decade.1

It can be a very frustrating condition for you and a very uncomfortable condition for your dog. However, it is preventable and treatable.

Here’s what you need to know about flea allergies in dogs—from how they start to treatment and prevention.

What Is Flea Allergy Dermatitis in Dogs?

Fleas take their first blood meal on the host (your dog) within minutes of contact.2 When a flea feeds, it injects its saliva into your dog’s skin. This saliva contains enzymes, peptides, and amino acids. It also contains histamine-like compounds that trigger a release from the dog’s immune system.

Flea saliva can cause an inflammatory reaction in animals that are sensitive to it. Some dogs have an immediate hypersensitivity to it within 15 minutes, while others have a delayed reaction that takes 24-48 hours.

Dogs with atopic dermatitis are more likely predisposed to developing flea allergy dermatitis (FAD).1

What if I Don’t See Fleas on My Dog?

Just because you don’t see the fleas, it does not mean they aren’t there.

A common misconception is that fleas are only a concern during warmer months. This is not true. Another misconception is that fleas can’t come inside your house. Fleas can live indoors as eggs, larvae, and pupae, and pets and humans can also bring fleas inside.

Signs of a Flea Allergy in Dogs

You may not see the fleas right away, but you will see the evidence of the allergic reaction. Even one flea bite can cause this allergic reaction.

When dogs feel flea bites, they often chew and bite at their rear by their tail and/or jump up from a resting position. If you see itching in your dog, and it leads to hair loss on the middle of the back to the tail base, you need to think flea allergy dermatitis. The hair loss can spread all over the body, up to the head and neck if left untreated.

When a dog scratches, licks, and chews, it breaks the skin barrier and can cause open sores and scabs. The licking and chewing can also cause ongoing moisture that can lead to yeast and bacterial infections.

Photo By: Sandra Mitchell, DVM

Photo By: Sandra Mitchell, DVM

How Does the Vet Diagnose a Flea Allergy in Dogs?

It is important to get a true diagnosis when a dog is itching severely.

Your vet will first look for any evidence of fleas or flea dirt (which is the flea excrement), sometimes using a fine-tooth comb.

It is common that a pet parent may not see the fleas at home on the pet, but veterinary staff are trained flea detectives who work hard to find them.

Tests can also be done to determine the underlying cause of the allergic reaction. Vets use blood tests and skin tests for flea allergies.

Skin testing, called intradermal testing, is usually performed by a veterinary dermatologist. A wheal (bump on the skin) forms on the skin, usually within 15-20 minutes of injected a small amount of an allergen into the skin.3

Blood testing can also be done in most general veterinary practices to test the IgE directed against the flea-specific salivary antigens.

Diagnosing the Secondary Skin Infections in Dogs

There is often a secondary infection that develops on a dog’s skin with FAD. Your vet can use cytology to diagnose any secondary skin infections.

Cutaneous cytology is a valuable diagnostic tool. Using a piece of tape to collect a surface sample from a skin lesion helps determine the type of microbial population as well as the inflammatory component present.4

It is quick and inexpensive. This helps guide the doctor to prescribe the most appropriate and effective treatment for the patient.

How Do You Treat Flea Allergy Dermatitis in Dogs?

The number one priority in FAD treatment is to kill the fleas! This means to kill them not only on your dog, but on all pets in the household and killing fleas in the environment.

Oral Flea Medications

Oral flea medications are going to provide the quickest demise of the fleas.

You can use a product containing Spinosad to kill all fleas on your dog within 30-60 minutes to give the quickest relief. Then you can follow up with a product that lasts 30-90 days.

Once the fleas are dead, it is a good idea to bathe the dog to get off all of the dead bugs and their excrement. You can get a medicated shampoo prescribed by your vet to soothe the skin, or you can find over-the-counter dog shampoos that contain oatmeal and pramoxine to help soothe the itch.

Skin Treatment

After the fleas are eradicated, you still need to treat the skin irritation caused by the allergic dermatitis.

In mild cases, you can treat your dog with Benadryl at home to stop the allergic reaction and provide relief from the itch.

Always check with your veterinarian for dosing instructions and to make sure this medication is safe for your pet.

Most dogs with FAD need more help, and you can talk to your veterinarian about the need for steroids or other allergy meds such as Apoquel or Cytopoint.

How to Prevent Flea Allergies in Dogs

As the saying goes, an ounce of prevention goes a long way. Preventing, reducing, and eliminating flea infestations is crucial to preventing recurring FAD.

Treat the Environment

Just treating your pet without treating the environment is only 50% of the problem. Indoor flea eradication measures include vacuuming (carpets, cushioned furniture, cracks and crevices on floors, and baseboards) and washing pet bedding in hot soapy water.

Treat Your Yard

Outdoor areas need attention, such as shaded areas around the house or your dog’s kennel or favorite sleeping area. You can use premise sprays for fleas indoors and out. For both the house and yard, you may need to contact an exterminator for the best method of flea removal.

Use Monthly Flea and Tick Preventatives

There are many flea prevention products on the market. Work with your veterinarian to pick the one that is best for your dog.

The oral medications in the isoxazoline category have been the most recent group that has been extremely effective and safe for most dogs. Talk to your vet to make sure your dog doesn’t have any contraindications such as seizures.

If you keep the flea population under control, you can spare your pet pain and suffering. It can take three months to rid your house of an infestation. It is time-consuming and expensive.

Prevent what you can to keep your dog flea-free!


Fritz, Anissa. Use this veterinary study to help clients take FAD seriously. January 27,2019.

Lam, Andrea and Yu, Anthony. Overview of Flea Allergy Dermatitis, Dermatology Compendium,Vol 31, No 5, May 2009.

Dryden, Michael. Flea Allergy Dermatitis.

Jangi Bajwa, “Cutaneous cytology and the dermatology patient”, The Canadian Veterinary Journal, (

Controlling Fleas and Ticks Around Your Home,

Kwocka KW. Fleas and related disease. Vet Clin North Am Small Ani Pract 1987;17:1235-1262


Stephanie Lantry, DVM


Stephanie Lantry, DVM


Dr. Lantry is a Milwaukee, Wisconsin native. She knew from a very young age that she wanted to be a veterinarian and worked towards that...

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