There are four major types of epidermolysis bullosa. The skin has a top or outer layer, called the epidermis, and a dermis layer that is underneath the epidermis. The basement membrane is where the layers of skin meet. Doctors determine the type of epidermolysis bullosa based on the location of the changes in the skin and the gene mutation identified. The types of epidermolysis bullosa include: Epidermolysis bullosa simplex: Blisters occur in the lower part of the epidermis. Junctional epidermolysis bullosa: Blisters occur in the top portion of the basement membrane, due to problems in attachment between the epidermis and basement membrane. Dystrophic epidermolysis bullosa: Blisters occur in the upper dermis due to problems in attachment between the basement membrane and the upper dermis. Kindler syndrome: Blisters happen in multiple layers of the skin, including the basement membrane. Researchers have identified more than 30 subtypes of the disease, which are groupings under the four major types of epidermolysis bullosa. By knowing more about the subtypes, doctors can focus treatment of the disease. A fifth type of the disease, epidermolysis bullosa acquisita, is a rare autoimmune disorder that causes the body’s immune system to attack a certain type of collagen in the person’s skin. Sometimes, it happens with another disease such as inflammatory bowel disease. Very rarely, a medication causes the disease. Unlike the other types of epidermolysis bullosa, the symptoms may begin at any age, but many people develop symptoms during middle age.