There is a group of diseases called pemphigus that have several forms (foliaceus, vulgaris, erythematosus, vegetans and bullous pemphigoid) and vary in location and severity. These diseases are an autoimmune process; the body's own immune system attacks the "cement" of the skin layers, creating blisters, sores, crusts, and ulcerations on the skin and mucocutaneous junctions (where skin meets mucous membranes, the moist tissues of mouth, nose, eyes, vulva/prepuce, and anus).
Pemphigus vulgaris, while more rare than other forms, is specific for the mucocutaneous junctions, such as lips. The skin may also be affected, usually mildly involved.
Ulcers and sores resulting from these diseases can become secondarily infected with bacteria, creating more of a problem. Antibiotics will help, but will not cure this condition, which is caused by an "overactive" and errant immune system.