When pressure inside the cranium is increased, pain-sensitive structures in and around the brain are distorted and cause pain to be felt in an ill-localized area but often identifiably at the front or back of the head. This traction headache is potentially serious, since it may be caused by brain swelling, infection, bleeding, tumour, or obstructed flow of cerebrospinal fluid. Also, pain may be felt in the head region although the disorder causing the pain is situated elsewhere; an example is the facial pain sometimes felt with lack of blood to the heart. Local disease of such cranial structures as the jaw joints, the paranasal sinuses and teeth, the middle ear, and the skull bones themselves may also generate pain, requiring a careful, probing history in order to be identified as the cause of the headache.