Pemphigus ( or ) is a rare group of blistering autoimmune diseases that affect the skin and mucous membranes. The name is derived from the Greek root pemphix, meaning "pustule".

In pemphigus, autoantibodies form against desmoglein, which forms the "glue" that attaches adjacent epidermal cells via attachment points called desmosomes. When autoantibodies attack desmogleins, the cells become separated from each other and the epidermis becomes detached, a phenomenon called acantholysis. This causes blisters that slough off and turn into sores. In some cases, these blisters can cover a large area of the skin.

Originally, the cause of this disease was unknown, and "pemphigus" was used to refer to any blistering disease of the skin and mucosa. In 1964, researchers found that the blood of patients with pemphigus contained antibodies to the layers of skin that separate to form the blisters. In 1971, an article investigating the autoimmune nature of this disease was published.