Colored sweat, as we discussed a few pages back, is unusual enough. Even stranger is a sweating condition called hematidrosis in which a person actually sweats blood. Some cases are caused by other diseases or high blood pressure, but most of 75 or so reported cases in the last hundred years have occurred while the person was experiencing extreme stress, anxiety and fear. A couple of examples: a prisoner sentenced to death and a person living in London during the Blitz.
According to former medical examiner and forensic expert Dr. Frederick Zugibe, hematridrosis is an extreme side effect of the fight or flight response. The anxiety and fear is so strong that it causes the small blood vessels supplying the sweat glands to tightly constrict, and then dilate so widely that they hemorrhage blood. The blood mixes with the sweat already being produced in larger amounts due to stress, and it appears as blood on the skin's surface. If it sounds painful, it is. Since the condition is so rare and the few who have exhibited the symptoms have generally only had one episode, bloody sweat remains a puzzle.