How, then to explain this phenomenon? Fraud certainly figures in some cases. Magdalena de la Cruz, the famous Spanish stigmatic of the 16th century whose frequent self-mortification and spectacular wounds made her a favorite at court, eventually confessed to having inflicted her own injuries. Similarly, Johann Jetzer, who claimed to have experienced not only recurrent poltergeist phenomena but also a series of religious visions, confessed in 1507 that his stigmata were fake. Four friars from his monastery were subsequently burned at the stake, and Jetzer himself escaped death only after his mother smuggled him a set of women’s clothes, in which he bluffed his way out of his death cell.
Aside from cases of outright fraud, which may well form the majority of all cases, the appearance of stigmata appears to be an essentially psychological condition whose manifestations are determined by the cultural expectations of the stigmatics themselves. A large number of sufferers seem to have displayed abundant evidence of low self-esteem, health problems, or a tendency toward self-mutilation - a potent mix when combined with exposure to the pervasive iconography of centuries of Christian tradition. It has been shown beyond a reasonable doubt that many have inflicted the five wounds on themselves, sometimes unconsciously, perhaps while in an altered state of consciousness brought on by extensive fasting or intensive prayer.
Read more: The Mystery of the Five Wounds | History | Smithsonian