Hair (as opposed to flesh) did not decay, and on the occasion when a saint was exhumed for the sake of retrieving relics (or simply proving sainthood by the belief that incorruptibility of the corpse was a divine sign) finding a good head of hair was proof and a relief. Locks of hair counted as relics.* The earliest reference to this was in the 4th century, when an early martyr named Nazarius was disinterred and discovered to have a full head of hair.
The first Christian king of Norway, Olaf Tryggvason, was a cruel man to those who would not accept forced conversion, but a year after he died he was exhumed and found to have hair and nails that had continued growing "as much as when he had been alive." (Presumably, this means twice as long as when he died.)** His beard and hair were trimmed and put into a fire to see if they were suitable as relics. When the hair did not burn, the presiding bishop declared Olaf a saint.
Hildegarde of Bingen was a cloistered nun who was recognized in her life as very wise and holy. A single hair of hers was preserved in a silk container the altar at her abbey. A fire that swept through the church left her relic unharmed. This hair had other powers: when a woman who was possessed by a demon had the hair brought before her, the demon fled.
Jacques de Vitry wrote a biography of a Beguine, Marie d'Oignies. During her life, a man whose illness could not be diagnised after seeing many doctors was cured by the touch of Marie's hair.
The illustration is of the Talisman of Charlemagne, an amulet carried by him that supposedly carried a hair of the Virgin Mary.
Jacques de Vitry left behind several writings, but only the one biography. What was it about Marie d'Oignies that made her a special interest? He was fascinated by the "holy power" of the Beguines, and Marie was a singular member. We'll take a look at what made her special next time.
*Teeth and fingernails were also desirable, since they could be taken without desecrating the body; in later centuries, of course, the entire skeleton became fair game.
**And you know that hair and nails do not continue to grow after death: the skin shrinks and pulls back, revealing more hair/nail from under the surface.
