The flea is often a nuisance to owners and our cats and dogs friends when they have them. In addition to leading to anemia and carrying other diseases (such as intestinal parasites - dipylidium, which lives inside the flea), they can cause a dermatological condition called Dermatitis allergic to flea bite (DAPP).
DAPP is a very common condition that results from a hypersensitivity / allergy to the components present in the saliva of fleas, therefore not tolerating their bites.
In addition to the typical itching, which is manifested in biting, scratching and rubbing caused by the presence of fleas, when the animal has DAPP, it also presents hair loss (alopecia in characteristic areas - image), sometimes with crusts and inflammation. In recurrent cases they may suffer from skin peeling, keratinization, hyperpigmentation and make the skin thicker.
As they are already traumatized areas, they can lead to infections by opportunistic bacteria.
As for treatments unfortunately there is no cure but it can be improved by trying to avoid as much as your animal is bitten, making flea control on the animal and the environment as effective as possible (using deworming and repellents) and additionally it will always be beneficial the use of fatty acid supplement. In case of infection and inflammation, medical treatment and follow-up may be necessary.