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  • Victoria D., RVT

Why Fleas Can Make Your Pet So Itchy

Ever wondered by fleas make your pets so itchy? It's usually due to something called flea allergy dermatitis, or FAD. FAD occurs when your dog or cat has a reaction to the saliva from flea bite. This condition is also known as flea bite hypersensitivity and is the most common dermatologic disease in household dogs in the US.

Signs of Flea Allergy Dermatitis

Clinical signs can vary, from occasional scratching to hair loss (alopecia) and skin lesions in worse cases. Pets with frequent exposure to fleas or an underlying condition or skin disease will have more extreme signs. We tend to see the most sensitivity in dogs’ flanks, hind and middle thighs, lower belly area, lower back, neck, and ears. FAD is typically diagnosed based on the pet’s history, the presence of clinical signs, and visible fleas or flea dirt. FAD can also be diagnosed via intradermal allergen testing (IDAT) though this isn’t typically needed.

Cases increase in the late summer and in warmer climates which corresponds to peaks in flea populations. Your pet's history can be imperative for diagnosing pets who have recently traveled, been to a daycare or boarding facility, and have known allergies. Seeing actual fleas on the infected pet is extremely helpful in the diagnosis and is a great teaching moment for pet parents. Your vet will be able to show you how to check your pets fleas in the future. To check your pet, slowly part the hair against the normal direction it lays to reveal flea dirt (dark reddish/brown excrement left behind) or the fleas themselves. It is also essential to understand that only a few bites are needed to warrant a reaction in some animals. Hence, visible fleas on the pet aren’t always necessary, especially in hypersensitive animals.

Treating Flea Allergy Dermatitis

Treatment of FAD typically takes two phases. First, fleas must be eliminated on the pet and in the home environment. Even if the fleas are killed on the pet, if there is an existing infestation in their environment, they are likely to have subsequent infections even while remaining on monthly flea preventatives. The best way to manage fleas would be to speak to your veterinarian about a monthly topical or oral systemic prevention for your pet and keep them on it year-round. Combining the preventatives given to your pet with repeated application of insecticides to their environment has proven to be the best method to prevent future infestations.

The second step, which will likely happen concurrently with the first, is to treat the itching and secondary skin infections due to the FAD. Systemic antimicrobials are commonly used to help control the affected areas and reduce inflammation. Additionally, corticosteroids have proven to be effective at controlling intense itching. They are often given orally, so doses may be tapered as directed by the veterinarian.

Treatment will not immediately eliminate any present flea infestations and subsequent reactions. Depending on how many fleas are living in the pet’s environment, it can take 1-3 months to completely eliminate the fleas. The most effective long-term flea control is preventing fleas from reproducing and creating future infestations. Therefore, lifelong flea control via oral or topical application to our pets is recommended, even after the issues have subsided.


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