Bullous pemphigoid is a skin condition that causes large, fluid-filled blisters that develop on areas of skin like the upper thighs, lower abdomen, or armpits. The condition is more prevalent in older adults. It occurs when the immune system attacks a thin layer of the tissue below the skin’s outer layer. The reason for this unusual immune response is not known. But in some cases, it could be the result of certain medications.

The body’s immune system usually produces antibodies to fight bacteria or other potentially harmful foreign substances. But for unknown reasons, the body may develop antibodies to a specific tissue in the body. In bullous pemphigoid, the immune system produces antibodies that connect the skin’s outer and next layers. The antibodies lead to inflammation that causes blisters and itching.