Flea Allergy Dermatitis (FAD) in Cats


Flea allergy dermatitis (FAD) is a skin disease that results when a cat develops an allergy to flea saliva. The body treats the allergen as a harmful substance and reacts disproportionately. Note that FAD is distinct from a flea infestation and not all cats who have fleas have FAD.

FAD is the most common skin disease in cats. An allergic cat will be very itchy, often leading to obsessive grooming and scratching. This excessive scratching can develop into a rash characterized by hair loss, red skin, and scabs. Once the skin is inflamed, secondary bacterial and fungal skin infections are common complications. Other skin conditions can create similar rashes, so basic diagnostic tests like a skin scrape and fungal culture are performed to rule out other potential causes. Lack of evidence of fleas does not rule out flea allergy because it only takes a few flea bites to trigger the allergy. It can be difficult for a pet parent to know if a pet's itching is triggered by flea bites, as cats may remove all evidence of fleas by consuming them as they groom.

Consistent, year-round use of veterinary-approved flea control products is the best way to prevent flea allergy dermatitis. Pet owners should consistently use flea control year round as a preventative measure. Always consult a vet before choosing preventative flea control. There are many products on the market which are neither safe nor effective, especially for cats.

Risk Factors

Fleas are parasitic insects that are active year round and worldwide. All housepets are at risk of coming into contact with fleas at any time. The presence of fleas on a cat does not necessarily mean that the cat has FAD, but flea allergy is the most common skin disease in domestic cats.

FAD symptoms are not an emergency, but veterinary care is recommended to ensure the condition does not worsen or develop into secondary infection.

The severity of symptoms of FAD is proportional to the level of exposure to fleas. Most cats improve quickly with treatment and symptoms are easily managed by maintaining year-round preventative flea medication. The sooner treatment is started after the onset of symptoms, the less likely secondary skin infections are to occur.

Other factors that increase the risk of flea exposure and subsequent FAD include:

• Frequently going outdoors • An outdoor pet in the home • Living in an apartment building with many pets

• Pet parents with an outdoor profession

Possible Causes

Flea allergy dermatitis is caused by an allergy to flea saliva. An allergy results when a substance is incorrectly identified as harmful by the immune system. Histamine is then released, inducing symptoms characterizing an allergic reaction like redness, swelling, and itch.

Main Symptoms

The main symptoms of FAD in cats are:

Itchiness • Obsessive licking • Excessive scratching • Hair loss • Red skin • Scabs • Skin inflammation

Detailed Characterization

The severity of the FAD symptoms will increase if the cat has been exposed to many flea bites and if treatment is not started promptly. If the cat is grooming and scratching itself excessively, secondary skin infections can develop.

If secondary bacterial or fungal infections of the skin occur, other symptoms will develop:

• Thickened, gray skin (lichenification) • Crusty skin • Pustules • Weeping or draining sores • A foul odor to the skin

Testing and Diagnosis

Diagnosis begins with a physical examination and a thorough history. The absence of evidence of fleas does not rule out flea allergy as the cause of the dermatitis. A large flea population is not necessary to trigger the allergic response, and fleas are often groomed out of the fur. 

Since there are numerous reasons a cat may be itchy or have a rash, a skin scrape and fungal culture are performed to eliminate other possible causes. Flea control is the cornerstone of both therapy and prevention for flea allergy dermatitis. Other treatments for the immediate symptoms of FAD may include: 

• Antibiotics • Antifungals • Steroids 

depending on how severe the symptoms have become prior to treatment.

Consistent, year-round use of veterinary-approved flea control products is the best way to prevent flea allergy dermatitis. It is critical to ensure that all products used are cat-safe, even if they are used on the environment or other types of pets who may come into contact with the cat. Cats are more sensitive to pesticides than other species, so professional guidance in selecting products is critical.

Steps to Recovery

Once an allergy is established the goal is to prevent exposure, as there is no cure for the allergy itself. 

Severely itchy cats may require short-term use of steroids for relief. Secondary bacterial or fungal skin infections require treatment with appropriate antibiotics or antifungals. Cats usually respond favorably to aggressive treatment, but it may take months for hair to grow back. 

Cats with FAD who are kept on year round preventative flea medication are expected to make a full recovery. The chance of relapse depends on whether the cat is exposed to fleas again in the future.


Flea allergy dermatitis is not contagious, but fleas can carry infectious diseases of concern to humans as well as cats. 

Preventing flea bites is the cornerstone of treatment for flea allergy dermatitis. In addition to maintaining a vet-approved external parasite control program, early detection of fleas and other parasites is fundamental to addressing symptoms promptly.

Is FAD Common in Cats?

Flea allergy dermatitis is the most common skin disease in cats. However, preventative anti-flea methods greatly decrease the risk of symptoms ever occurring or developing into secondary infections.

Typical Treatment

FAD treatment depends on the severity of symptoms when treatment begins. Treatment may include:

• Veterinarian approved flea control • Antibiotics • Antifungals • Steroids

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