a chronic, generalized skin disorder characterized by an eruption of serum-filled vesicles (blisters). These vesicles form under the epidermis, the outermost, nonvascular layer of the skin, and have walls of stretched epidermal cells. The cause of bullous pemphigoid is not known. It occurs predominantly in elderly adults. Although debilitating, it is not fatal and responds well to treatment with corticosteroids.