Pyoderma describes any skin infection that is pyogenic, meaning there is local inflammation serious enough to cause the production of pus. It may be caused by an infectious agent such as bacteria or fungus or, rarely, it can signal an autoimmune problem.
Pyodermas are classified by the extent and cause of the infection and whether they are primary or secondary. A superficial infection affects the upper layers of skin and hair follicles. When the infection reaches deeper, it is a deep pyoderma. Pyodermas are also classified by the causative bacteria. A pyoderma that results from another condition is called secondary pyoderma.
Bacterial Pyoderma
Many bacteria are normally present on skin, including several types of Staphylococcus, or "staph." A break or abrasion in the skin can provide an entryway to the body for these surface bacteria, and they stick very well to the moist edges of a cut. The bacteria begin to multiply and to extend into the cut. The body's defense mechanism includes bringing immune cells into the area to fight the bacteria. Eventually, accumulation of these cells produces the thick whitish liquid that we call pus.
Lick Pyodermas
When a dog licks itself excessively, pyoderma can eventually develop. As the dog licks its skin, irritation can become severe enough to cause a break in the skin. Bacterial infection may arise at the site, leading to the development of pyoderma. There are several possible causes of excessive licking, including itching that accompanies a skin allergy, trauma to the area, "hot spots," or pain.
Other Causes
In dogs, the other common causes of pyoderma are flea bites that become infected, and poor grooming leading to matted hair that irritates the dog's skin. Occasionally, an underlying disease is present, such as hypothyroidism or hyperadrenocorticism (Cushing's syndrome). These diseases cause changes in the skin that make it more susceptible to infection.
