First, let's talk about the failure to properly apply flea control products. Often owners don't understand when and how to apply the topical flea control products. A good rule of thumb is to remember to wait at least two days after a bath before applying the product and to wait at least two days after applying the product before giving a bath. The products use the oil glands associated with the hair follicles for absorption into the skin. Most shampoos strip these glands of their oil. Therefore, waiting a few days after the bath will allow the oil glands to replenish. By the same token, it takes a few days after applying the product before it is completely absorbed into the skin. Therefore, the product needs time to absorb before allowing your pet to get wet. This two-day rule also applies to swimming. If your dog is a frequent swimmer, then I suggest using an oral flea control product and avoiding the topical products altogether.
Another application error is failure to apply the product directly to the skin. To apply properly, part the hair, put the end of the tube against the skin, and then squeeze out the liquid. Don't touch it! I have had several clients who have told me they "rubbed it in." Don't! That only takes the product off your pet and onto you. Also, with cats, it is important to apply it to a part of the head they can't reach with their tongues. Cats are notorious for bathing the products off.
Another possible reason for your pet’s flea allergy dermatitis is that some dogs and cat are extremely sensitive to fleabites. Some animals are so allergic that one fleabite can cause them to itch for an entire week! Therefore, you may never see the flea that is causing the allergy. It is essential to limit the amount of time these animals spend outside in order to limit their possible exposure to fleas. Also, it is especially important to keep them on a flea control product all year round.
Finally, a common mistake I see pet owners make is to only treat their outdoor pets and not the pets that live indoors. I see this most often with owners who have indoor cats and indoor/outdoor dogs. They treat the dogs for fleas, but not the cats. The problem with that is the fleas will hitch a ride on the indoor/outdoor pet. Once they get inside, they will jump off the animal that has been treated and onto the one that hasn’t.
Diagnosis of flea allergy dermatitis is pretty straightforward. Typically, a distinct pattern of hair loss and redness of the skin appears on the animal’s rump. The pets are usually very pruritic (itchy) and will bit and scratch at the base of the tail. If your dog is showing these symptoms, then it is almost certainly fleas. Look very carefully, and you may spot one.