Pemphigus is an autoimmune disorder that happens when the immune system attacks healthy skin. Immune molecules called antibodies target proteins called desmogleins, which help link neighboring skin cells to one another. When these connections are broken, skin becomes fragile and fluid can collect between layers of cells, forming blisters. Normally, the immune system protects the body from infection and disease. Researchers do not know what causes the immune system to turn on the body’s own proteins, but they believe that both genetic and environmental factors are involved. Something in the environment may trigger pemphigus in people who are at risk because of their genetic makeup. In rare cases, pemphigus may be caused by a tumor or by certain medications.