Pemphigus Vulgaris is one of a group of rare, relapsing auto-immune diseases causing blistering of the skin and mucous membranes (eg mouth, nose, throat and genitals). In pemphigus disorders the immune system makes a mistake, views cells in the skin and mucous membranes as foreign and an immune response is triggered. Affected individuals have high concentrations of antibodies produced by the immune system. These bind to a specific protein in the skin (desmoglein 3 and sometimes desmoglein 1), causing interference with the skin's normal function. The cells no longer stick together and become separated from each other. This causes the burn-like lesions or blisters that are typical of PV. Symptoms often occur first in the mouth, but lesions can cover a significant area of skin. The disease is non-infectious.

Although it is known that desmoglein antibodies cause PV, it is not known why people develop these autoantibodies in the first place. Genetic factors are believed to be important but it is likely that there are other factors which help trigger PV.