It is not surprising to find the mysterious phenomenon of menstruation involved in all sorts of superstitions and religious beliefs. Probably the most widespread assumption which permeated religious rituals and led to the establishment of curious customs associated with the menses was that menstruation periodically rids the body of woman of something undesirable that has accumulated in the organism, more specifically in the blood. To some it thus was a mechanism for removing an excess of nutriment from the body. According to the Mosaic law the mystery represented a process of purification: the impurities collected in the woman's blood were discharged in the menstrual flux, so that she underwent a recurring series of purifications. To the men of the monasteries, says Crawfurd,3 menstruation was a symbol of the essential sinfulness and inferiority of women, polluted alike and polluting.
It is not difficult to trace a relationship between such ideas
SUPERSTITIONS CONCERNING MENSTRUATION. JAMA. 1916;LXVII(4):289. doi:10.1001/jama.1916.02590040043014