Pemphigus is an autoimmune disease in which the body attacks the connections between its own skin cells, causing blisters to form on the skin and mucus membranes. Autoimmune diseases result when the body’s immune system does not recognize itself. Cells that normally attack invading viruses and bacteria begin attacking the body’s own cells, causing damage. The term pemphigus comes from the Greek word for pustule (a blister on the skin that is filled with pus).