Flea Allergy Dermatitis in Cats and Dogs

Amy Shojai, CABC

For some pets, fleas are an itchy aggravation, crawling through fur and biting their hosts. Some cats and dogs don't seem bothered at all by fleas. And then there are those who develop flea allergy dermatitis (FAD). Although not fatal, FAD can be extremely harmful to your pet. Here's how to recognize and treat FAD.

What Is Flea Allergy Dermatitis?

The immune system protects the body from foreign invaders, such as viruses and bacteria. Sometimes, your pet's immune system overreacts to otherwise harmless substances. That causes an allergic reaction inside the body or on the skin.

FAD most commonly affects dogs and cats. One study showed a 13% increase in FAD in dogs over the past decade.1 Antigens (toxins) or proteins in the flea saliva cause an allergic reaction. Your pet's antibodies don't recognize these substances and attack them. The overreaction to allergens causes the allergy symptoms.

It's the exposure to the allergen that first primes the body's immune system to overreact. A dog or cat never exposed to fleas won't get itchy with the first bite. Instead, pets develop an allergic response with each exposure. Dogs inherit the tendency to develop allergies, so the "itch factor" occurs more often within certain breeds. Still, any cat or dog can develop FAD. Once primed, it only takes one bite to provoke all-over itching for up to two weeks.

Also, pets often suffer from more than one kind of allergy. They can get itchy from both fleas and inhaled pollen, for example, making the itching that much worse.

Symptoms of Flea Allergy Dermatitis

Dogs and cats with FAD develop obvious symptoms. It only takes one or two bites for a reaction that can last two weeks. Flea bites get larger, and they turn into sores when your cat or dog scratches.

Once your dog or cat has scratched for a long period, the rash sometimes looks like other skin conditions. Therefore, your veterinarian must diagnose FAD, or any skin ailment, to prescribe proper treatment. You should watch for these common signs and alert your vet if necessary.

Constant Scratching

Any pet with fleas will scratch at irritated areas. But allergic pets get no relief from scratching. The itch drives them crazy. They scratch so long and so hard that they hurt their skin.

Animals with FAD focus on different areas of the body. Dogs with FAD scratch, bite, and lick at their backs, tails, groins, and thighs. You'll see sores, crusty skin, and thinning fur in these areas. Cats with FAD scratch at their ears, head, neck, and back. Cats often dig deep wounds into their skin, especially behind the ears.

Skin Sores

Flea bites first look like small, flat reddish spots. This is called a macule. With allergic reactions, the bite turns into a small, firm, pink or red elevation of the skin that looks like a pimple. This is called a papule. If you have a cat, she may develop a rash of tiny reddish scabs beneath your cat's fur, sometimes all over her body.2

Trauma from scratching turns lesions into chronic symptoms. You'll see scaly skin, excoriation (scratching off the skin surface), and scabby skin. Hyperpigmentation (darkening of skin color) can develop when licking stains the skin.

The constant scratching predisposes pets to bacterial infections. Dogs with FAD often develop hot spots. This moist, red spot of inflamed skin feels hot to the touch and spreads fast. Hot spots turn your dog's sensitive skin into an excruciating sore that he won't let you touch.3

Cats may develop an eosinophilic granuloma complex, sometimes called lick granulomas. An itchy area of elevated, bright red oozing skin appears on the inside of your cat's thighs or abdomen. Yellow to yellow-pink raised sores appear in straight lines on the back of both hind legs.

Thinning Fur

Dogs and cats that are suffering from FAD often lose hair because they are constantly licking, gnawing, and scratching. This causes their fur to loosen, thin, or break. You can often see the skin through the hair coat, especially in the areas of the body where fleas prefer to feed.

Managing Flea Allergy Dermatitis

A veterinarian should formally diagnose any allergy in your cat or dog. That way, they can prescribe a custom treatment plan. At-home treatments can address the symptoms, but your doctor has more effective targeted options with prescription medication. Medications can block the release of inflammatory chemicals and prevent itching.

Cortisone, for example, is a steroid that can kill the itch and help your pets' adrenal glands kick into action. Antihistamines are usually prescribed to treat or prevent allergies, as they also relieve itching. Antibiotics can help treat any infections and inflammation that might pop up from incessant scratching.

Getting rid of the irritant causing FAD — the fleas — is the first step in treating it. Moderate to severe infestations may take several months to get under control. The cure won't come overnight. It takes up to two weeks for itching to resolve once you banish the fleas.

You can relieve your pet's discomfort with home care.

Bathe Your Pet

Bathing your pet can help reduce the itch threshold and soothe sore spots on their body. Bathe your pets every day for two or three days. Avoid hot or warm water. A cool water rinse is best for relieving itchiness. Make that part of your grooming routine.

Adams Pet Care offers a wide variety of flea and tick cleansing shampoos for cats and kittens, for dogs and puppies, and for pets with sensitive skin. Adams Pet Care also offers sprays, topicals, and pyrethrin dip.

If bathing your pet doesn't help, you'll need to see a veterinarian. Prescription shampoos containing antibiotics or other medications may help.

Fatty Acid Supplements

Omega-3 and omega-6 fatty acids help reduce itching and inflammation. Find these supplements at health food or pet supply stores, or get them from your veterinarian. Pungent fishy ingredients contain potent levels of fatty acids. Many pets gulp them down like treats.

Making Flea Treatment a Priority

If your pet suffers from FAD, it's best to plan ahead. Get veterinary help and use home care treatments to relieve the itch. But also get rid of the bugs on your pets and in the environment. Only a fraction of the flea population lives on your cat and dog. The remaining life stages hide out in your house and yard.

To end flea infestations in your home, try an Adams™ Pet Care spray or fogger. For regular treatment of the outside environment, try an Adams™ Pet Care yard and garden spray. Pay special attention to the doghouse and the shaded moist areas with organic debris, like mulch.4 This way, you can prevent your pets from picking up new flea hitchhikers and ensure they stay itch-free.

1. Lantry, DVM, Stephanie. PetMD. "Does Your Dog Have a Flea Allergy?" Feb. 8, 2021.https://www.petmd.com/dog/conditions/skin/c_multi_flea_bite_hypersensitivity

2. Cornell Feline Health Center. "Flea Allergy," 2016. https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/flea-allergy

3. Hunter, DVM, Tammy & Ernest Ward, DVM. VCA Hospitals. "Flea Allergy Dermatitis in Dogs," 2022. https://vcahospitals.com/know-your-pet/allergy-flea-allergy-dermatitis-in-dogs

4. Gardiner, John. UC Davis Veterinary Medicine. "Fleas," April 11, 2019. https://healthtopics.vetmed.ucdavis.edu/health-topics/canine/fleas


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