The cause of bullous pemphigoid is not well understood. The blisters occur because of a malfunction in the immune system.

Your body's immune system normally produces antibodies to fight bacteria, viruses or other potentially harmful foreign substances. For reasons that are not clear, the body may develop an antibody to a particular tissue in your body.

In bullous pemphigoid, the immune system produces antibodies to the skin's basement membrane, a thin layer of fibers connecting the outer layer of skin (epidermis) and the next layer of skin (dermis). These antibodies trigger inflammatory activity that produces the blisters and itching of bullous pemphigoid.

Contributing factors

ullous pemphigoid usually appears randomly with no clear factors contributing to the onset of disease. A small percentage of cases may be triggered by certain medical treatments, such as:

  • Medications. Prescription drugs that may cause bullous pemphigoid include penicillin, etanercept (Enbrel), sulfasalazine (Azulfidine) and furosemide (Lasix).
  • Light and radiation. Ultraviolet light therapy to treat certain skin conditions may trigger bullous pemphigoid, as can radiation therapy to treat cancer.
Nov. 21, 2012