The primary feature of bullous pemphigoid is the appearance of large blisters that don't easily rupture when touched. The fluid inside the blisters is usually clear but may contain some blood. The skin around the blisters may appear normal, reddish or darker than usual. Some people with bullous pemphigoid develop an eczema or hive-like rash rather than blisters.
In most cases, the blisters appear on the lower abdomen, groin, upper thighs and arms. Blisters are often located along creases or folds in the skin, such as the skin on the inner side of a joint.
The affected areas of skin can be very itchy. You might also develop blisters or sores in your mouth. If the mucous membranes of your eyes and mouth are primarily where your blisters are concentrated, this type of condition is called mucous membrane pemphigoid. If you develop blisters on your eyes, you're more likely to have scarring. This condition requires prompt diagnosis and treatment.
When to see a doctor
If you develop unexplained blistering — a condition not caused, for example, by a known skin allergy or contact with poison ivy — see your doctor.
The cause of bullous pemphigoid is not well-understood. The blisters occur because of a malfunction in your 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 fibers that connect the outer layer of skin (epidermis) and the next layer of skin (dermis). These antibodies trigger inflammation that produces the blisters and itching of bullous pemphigoid.
Bullous 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.
Bullous pemphigoid most commonly occurs in people older than age 60, and the risk increases with age.
If ruptured blisters become infected, this can lead to sepsis — a potentially life-threatening blood infection that affects your entire body. Sepsis is more likely to occur in older adults who are in generally poor health.
Rare forms of bullous pemphigoid involving the mucous membranes of the mouth or eye can lead to scarring.