 Occasionally, the blister fluid becomes blood-tinged.The blisters are tense, about 1–4 cm in diameter, leaving eroded and crusted areas, together with urticarial and infiltrated papules and plaques in an annular or figurate pattern.Homology between bullous pemphigoid antigens in the skin and neuronal antigens in the central nervous system has been proposed as a cause for the observed link between bullous pemphigoid and neurologic disease, along with a genetic predisposition.