Ritual purification is a feature of many religions. The aim of these rituals is to remove specifically defined uncleanliness prior to a particular type of activity, and especially prior to the worship of a deity. This ritual uncleanliness is not identical with ordinary physical impurity, such as dirt stains; nevertheless, body fluids are generally considered ritually unclean.

Most of these rituals existed long before the germ theory of disease, and figure prominently from the earliest known religious systems of the Ancient Near East. Some writers remark that similarities between cleansing actions, engaged in by obsessive compulsive disorder sufferers and those of religious purification rites, point to an ultimate origin of the rituals in the personal grooming behaviour of the primates, but others connect the rituals to primitive taboos.

Some have seen benefits of these practices that as a point of health and preventing infections especially in areas where humans come in close contact with each other. While these practices came before the idea of the germ theory was public in areas that use daily cleaning, the destruction of infectious agents seems to be dramatic.