Flea bite dermatitis is a skin condition in animals allergic to flea saliva. Flea saliva contains more than fifteen different substances that could provoke an allergic reaction in animals. Flea bite dermatitis can be caused by only one flea, since the bite of even this one flea is able create a severe allergic response and prolonged scratching in animals.

Like a mosquito, a flea feeds on blood, but whereas a mosquito feeds once, the flea continually feeds on the animal's blood. The flea droppings contain the blood that supplies young fleas with the iron and protein they need for growth. Most animals do not have allergies to flea bites and will not have excessive itchiness or skin lesions. Usually, the only way you can spot a flea infestation in animals without flea bite dermatitis is by noticing dark specks in the coat.

Fleas are the most prevalent in summer and fall, so the highest number of flea bite dermatitis cases occurs during these seasons. One female flea usually lays over 2,000 eggs, even though she is likely to live less than two months. An animal with flea bite dermatitis experiences extreme itchiness and often chews at the base of the tail and the feet, where flea bites are likely to occur. The stomach and inner thighs are also common sites for flea bites.

Besides severe itchiness, the thickening of the skin is a common sign of flea bite dermatitis. Flea bite dermatitis can also cause tiny red bumps on the animal's skin. Many of the worst cases of flea bite dermatitis involve reddening of the skin which signals extreme sensitivity to flea bites. Swelling may also occur.

All breeds of dogs and cats are susceptible to flea bite dermatitis, but flea bite dermatitis is more likely to occur in young animals rather than in puppies or kittens and older animals. A veterinarian can diagnose flea bite dermatitis with an intradermal allergy test. The vet injects a little of the flea antigen into the animal's skin and observes what happens to the skin. Basic blood tests are usually less accurate than the intradermal allergy test in diagnosing flea bite dermatitis.

Cool, not cold, water baths may help a dog suffering from flea bite dermatitis. The veterinarian will often prescribe hydrocortisone for dogs and cats with flea bite dermatitis in order to help stop some of the itching and redness of the skin. The animal should be monitored for secondary infections as the scratching tends to open up the sores further and leaves them open to other infections.