What is it?

Bullous pemphigoid is a rare skin condition that causes large, fluid-filled blisters. They develop on areas of skin that often flex- such as the lower abdomen, upper thighs or armpits. Bullous pemphigoid is most common in older adults.
Bullous pemphigoid occurs when the immune system attacks a thin layer of tissue below the outer layer of skin. The reason for this abnormal immune response is unknown, although it sometimes can be triggered by taking certain medications.