When this occurs, the skin reacts dramatically to the presence of Staph .
Bacterial hypersensitivity causes the skin to become very red.
Pustules and large vesicles filled with fluid develop on the skin. There is severe itching, and many dogs will cause further damage to their skin through scratching and biting. Bacterial hypersensitivity is diagnosed through bacterial culture and examination of a biopsy sample. Microscopically there are certain unique changes in the blood vessels of the skin in bacterial hypersensitivity. An intradermal allergy test may also be helpful.