Pemphigus foliaceus (PF) is an autoimmune blistering skin disorder characterized by an exfoliative dermatitis. It is the result of a type II hypersensitivity, in which auto antibodies turn against the cell membrane of the horse's epithelial cells. There are two main forms of PF, each associated with the specific area of the body affected. When PF affects the horse's skin, is is referred to as Pemphigus foliaceus. When the horse's mucous membranes and areas around the mouth, eyelids, vulva or anus are affected, it is called Pemphigus vulgaris. Pemphigus vulgaris is the more common form of PF seen in horses.

• Pemphigus foliaceus: In this form of PF, horses develop tiny skin blisters which eventually peel off, revealing large areas of hair loss and gray, flaky skin. The coronary band is also frequently affected, as PF affects the horn production of hoof material. This results in increasingly poor hoof quality and causes the hoof wall to flake off and lose its shiny appearance. Many horses also develop stocking up-like symptoms where their legs fill up with fluid, causing stiff and painful movement.
• Pemphigus vulgaris: Horses which develop this form of PF, which is the rarer form, develop burn-like lesions or blisters on the skin and mucous membranes (mouth, throat, genitals, eyes, nose).

Horses that develop the disease early in life (less than five years of age) tend to have a better chance of successful treatment.