Is Your Dog or Cat Scratching? It Could Be a Pet Flea Allergy

Posted - May 13, 2021

By Patricia Thomblison, DVM, MS

Allergic pets often have dermatologic problems with itchy reddened skin. Allergies can be due to a number of things such as the environment, food, and even fleas. Not all pets are allergic to fleas, but if they are they can be miserable, and no pet parent wants to see or hear the scratching and biting that can ensue.


Fleas are one of the most common parasites of dogs and cats and an allergic response to the flea bite can occur in young and old alike. Flea allergy dermatitis (FAD) causes intense itchiness, and you may see your pet scratch or grooming constantly. When fleas feed, they inject a tiny amount of saliva into the skin. The antigens in the saliva can cause an intensely itchy response.

Just a few flea bites can cause itching for days. You may not even see the fleas on your pet. Fleas spend most of their life off the host (dog or cat), so if the infestation is light you may not even find these pesky parasites on your pet. Your pet may spend a great deal of time grooming to try to rid itself of these annoying pests.


Dogs and cats with fleas will usually scratch, but if they have an allergic reaction the scratching becomes more severe. It is not unusual to see hair loss, especially along or near the tail, rump, and stomach, from the intense grooming. The skin may be reddened and have small pustules from secondary infections. Scratching and chewing are common causes of acute moist dermatitis or “hot spots” in dogs.

Cats may groom so much that the hair loss causes their stomachs to appear to have been shaved. In addition, cats may develop miliary dermatitis which is small scab-like lesions often around the head and neck. These lesions can be seen with any allergic response but are especially common with flea allergies.


A pet can itch for multiple reasons. Your veterinarian will use history and physical examination to help determine the cause. Other causes of intense itchiness in pets are scabies, mites, and food allergies, so it is important to make sure there are no other causes for your pet’s misery. Your veterinarian may look carefully for fleas and flea dirt (the excrement of fleas).

They may scrape the skin and look at the sample with a microscope to look for mites or other pathogens. Sometimes a biopsy may be helpful to determine the cause of dermatitis. If an allergy to food is suspected an elimination diet may be recommended.


The most important treatment for flea allergy dermatitis is to prevent flea bites. Good flea control is available, and your veterinarian can provide several options that can be safe and effective. It takes more than one application for flea control because of the nature of the flea life cycle.

Fleas live a large percentage of their life off the pet, so cleaning up the environment inside and outside is essential. This can include regular vacuuming, washing pet bedding, and cleaning other areas the pet spends time. Routine flea combing will help determine the effectiveness of the control program.


The itchiness may persist after the fleas are gone because of the damage to the skin. In extreme cases or if secondary bacterial infections are present the addition of steroids and/or antibiotics may be necessary. The use of these may be recommended at the initial onset but they are not without potential side effects.


Helping the skin heal and keeping the skin healthy can help make the pet more comfortable and lessen the chances of these problems. Skin topicals and shampoo therapy can help to calm and repair the skin and may prevent the need for more aggressive approaches. When selecting products, look for those with gentle soothing ingredients that will not cause additional irritation to the skin.

ZYMOX® Shampoo and Leave-On Conditioner have been shown to help dogs and cats. These products feature a patented enzyme formulation plus vitamin D3 for skin hydration. They also happen to be compatible with flea and tick topicals. Those painful hot spots may continue to need attention.

When this happens the ZYMOX Topical Cream and Spray with 0.5% hydrocortisone have antibacterial benefits and can reduce itching and inflammation. The line is available at veterinary clinics, pet specialty stores as well as authorized partners’ websites.

More information about flea control can be found on the Veterinary Partner and ASPCA websites.

Arden MooreClick here to read more about Dr. Patricia Thomblison

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