Pemphigus vulgaris

Pemphigus vulgaris is an autoimmune disease, which means the body's defense system picks the wrong target and attacks a part of the body itself. It's rare, although it's the most common of the different types of pemphigus. What it causes is blisters on the skin and on the mucous membranes, the moist lining of the mouth and other cavities of the body.

To see why, picture your skin cells, called keratinocytes, as if they were fastened to one another with snaps. Those snaps are the desmosomes, and the part that keeps them closed is called desmoglein, an adhesion protein, meaning a protein that holds things together. In pemphigus vulgaris, the body makes autoantibodies, antibodies aimed at its own tissue, and they latch onto the desmogleins. The snaps stop holding, the keratinocytes come loose from each other, and the skin splits open from the inside. That separation is called acantholysis, and it's what creates the blister, which breaks very easily.

In 80% of cases, it all starts in the lining of the mouth. There, the blisters tend to burst and leave painful erosions, which are shallow sores where the top layer has been lost. Skin lesions typically show up later.