A dog lying in the grass scratching its head.

Flea Allergy Dermatitis: A Single Bite Is All It Takes

Flea allergy dermatitis is the most common skin condition in dogs and a common cause of scratching and itching. But with flea control and prevention strategies in place, it doesn’t have to be the only thing on your dog’s mind.

Genetics Play a Role in Flea Allergy Dermatitis

The first thing to know about flea allergy dermatitis (FAD) is that it doesn’t affect all dogs. Only dogs genetically predisposed to FAD will develop symptoms when they are exposed to allergens in flea saliva. Other dogs will show no allergic reaction and will have just the usual itching associated with flea bites.

There are three antigens in flea saliva that trigger an immune system response, and in some dogs, that includes the production of antibodies. One of the antigens in flea saliva is a major allergen that produces an abnormally powerful response to something that the immune system would otherwise consider harmless. If your dog has environmental allergies, they are more likely to be allergic to fleas as well.

And dogs don’t have to be flea-infested to develop FAD; just one bite from one flea is all that’s needed. This makes a flea avoidance strategy critically important for dogs with FAD.

What Does FAD Look Like?

If your dog is itching and scratching above and beyond a “normal” scratching session, they may need to be checked for FAD. Dogs with FAD often have reactions along the back half of the body – from the middle of the back to the base of the tail and down the hindlegs. The intense itching caused by FAD can often mean dogs are missing hair in this area. In severe or untreated cases of FAD, the itching and inflammation may cause skin damage or open sores. This can lead to secondary bacterial and/or fungal infections, which leads to more scratching, gnawing and licking.

Diagnosing FAD Often Starts with Preventing It

If your veterinarian suspects FAD, often the first thing they will do is check for evidence of fleas. They may or may not find fleas and may find only flea dirt. Intradermal allergy tests similar to those done on people or specialized blood tests can confirm FAD. However, often a diagnosis is best confirmed by seeing a positive response to strict flea control.

Stop the Fleas, Stop the FAD

In some cases, dogs with FAD may need treatment to soothe their irritated skin and treat secondary infections. However, the best way to prevent and treat FAD is to remove the cause — fleas. If your dog has FAD, you should eliminate adult fleas from your dog and remove immature flea stages from your dog’s environment. Only 5 percent of fleas are adults at any given stage, the remainder are eggs, larvae (maggot-like stage) and pupae (cocoon stage). So it’s important to treat your dog, the inside of your house and possibly your yard and garden.

And remember that if one pet in the household has fleas, all pets must be treated with a flea control product to completely remove the flea infestation. It can take 3 or more months to completely rid a home of fleas.

Some vets recommend year-round flea control for dogs with FAD, even if there are no visible signs of fleas. There are numerous types of flea control products available, so talk to your veterinarian about which one may work well for your dog.

A Change in Diet May Help Skin Allergies

The food you feed your dog can positively or negatively affect your dog’s skin health and immune system. Dogs with flea allergy dermatitis or environmental allergies may benefit from food designed for sensitive skin. Ask your veterinarian if your dog could benefit from a sensitive skin formula.


A single flea bite can mean non-stop itching and scratching for dogs with flea allergy dermatitis. But eliminate the fleas and you eliminate the flea allergy dermatitis.


RELATED POST: Scratching at the Surface of Canine Skin Allergies

The information in this blog has been developed with our veterinarian and is designed to help educate pet parents. If you have questions or concerns about your pet's health or nutrition, please talk with your veterinarian.


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