Pemphigus foliaceus (PF) is the most common autoimmune skin disorder of both dogs and cats. While there is no sex predilection for this disorder, certain canine breeds are at risk for developing the disease. These are: Chow chow, Akita, Doberman pinscher, Schipperke, Newfoundland, and Spitz. It is unusual to see PF in a dog less than 2 years of age, although the majority of patients show signs of the condition before 5 years of age.

The lesions of PF consist of erythematous macules and papules that progress to pustules and eventually to crusts. The pustular stage is short-lived, so most affected patients present with a yellowish-brown crusting dermatitis. Clinically, the lesions themselves can be difficult to distinguish from lesions of bacterial pyoderma, however, there are several distinguishing characteristics. The first is the location of the lesions: with pemphigus, lesions often start on the face (periocular, bridge of nose) and pinnae, and progress to involve the trunk and foot pads (especially in the dog) or nailbeds and peri-areolar region (cats). Bacterial pyoderma rarely affects these areas. The second distinguishing feature is the actual lesion. With PF, pustules are often larger than pyoderma pustules, and while the latter are usually centered over a hair follicle (folliculitis), PF pustules may or may not be centered over a hair and can span several hair follicles. PF pustules are often surrounded by an erythematous halo, and may coalesce producing target or serpiginous lesions. PF and bacterial pyoderma both may have patchy alopecia and epidermal collarettes develop as secondary lesions. A final distinguishing characteristic is the condition of the pet. Dogs and cats with PF are often sick, febrile and inappetant, whereas most pets with pyoderma are not.

Besides bacterial pyoderma, other differentials for PF in the dog include: zinc responsive dermatosis, superficial necrolytic dermatitis (hepatocutaneous syndrome), dermatomyositis, mycosis fungoides, dermatophytosis, demodicosis, eosinophilic furunculosis, drug reactions, lupus erythematosus and pemphigus erythematosus. In cats, severe allergic (miliary) dermatitis and dermatophytosis can mimic PF.