Bullous pemphigoid is an acute or chronic autoimmune skin disease, involving the formation of blisters, known as bullae, at the space between the epidermis and dermis skin layers. It is classified as a type II hypersensitivity reaction. Clinically, the earliest lesions may appear urticarial (like hives). Tense bullae eventually erupt, most commonly at the inner thighs and upper arms, but the trunk and extremities are frequently both involved. Any part of the skin surface can be involved. Oral lesions are present in a minority of cases. The disease may be acute, but typically will wax and wane. Several other skin diseases may have similar symptoms.