It is an allergic skin disorder (dermatitis) which occurs when a dog or cat is hypersensitive to flea saliva. “Derm” means skin, and “itis” means inflammation. Flea Allergy Dermatitis is the most common allergy and cause of itching in dog, in fact,  the most common skin problems that affect pets are caused by fleas; it is common in the warm period of the year, so in countries with warmer climates it may persist all year round.

Flea Allergy Dermatitis or FAD is a very itchy and painful condition to your pet.


When a fleas feed, they bite a dog or cat and injects their saliva into the animal. Flea saliva contains many antigens (amino acids, aromatic  compounds, polypeptides, and  phosphorus) which some dogs and cats are very susceptible to. In an allergic reaction, the immune system overreacts and produces antibodies to a substance that it would normally tolerate (an allergic reaction to flea saliva, feces and exoskeleton occurs); this allergic reaction first of all is manifested as itch. As fleas need food to breed, they usually leave the dog or a cat after feeding (they do not lay eggs on a dog), you may think your dog doesn’t have flea infestation. Even a slight infestation, where a flea bites your dog few times in weeks, might trigger an allergic reaction, if a dog is sensitized; when the allergic reaction starts the bite site quickly becomes inflamed, red and itchy.  Due to itching pet damages itself by biting or chewing inflamed region repeatedly and for prolonged period, this may cause skin lesions and loss of hair in damaged areas.


FAD is easy to diagnose by clinical signs. The first symptom is severe itching and inflammation of the skin. Also observation of flea and flea feces is important in diagnosing flea allergic dermatitis. As mentioned above, by scratching affected areas pet may cause hair loss in the so called “flea triangle” - the region from the middle of the back to the tail base and down the rear legs, this is often associated with flea induced allergic dermatitis; in this area (and in the abdomen/umbilicus area also) pets affected by flea dermatitis may have various lesions, like: crusts, erythema, hot spots, salivary stains, excoriations, damaged and/or broken hair, hair loss, in severe cases skin in the damaged areas becomes thickened, dark. Secondary infections by bacteria and yeast are common in chronic and prolonged cases; bacteria and yeast are rubbed into the skin while animal is scratching, when they grow on the damaged areas an unpleasant odor may be present. Also due to the dogs ingesting the fleas that are intermediate hosts for the tapeworm Diplydium  caninum, most of the dogs suffering from FAD may have this parasite. Intradermal  skin test with flea antigen and IgE blood test maybe used to confirm flea allergy.

In order to treat FAD:

  1. Get rid of the fleas. Be sure to not only treat the animal, but also clean the environment your pet lives.
  2. Treat pet’s skin for itching, treat lesions.
  3. Treat pet’s allergy (with antihistamine).

Main Paige - WARNING: PETS Once they are in, they are in for life!