While menstrual flow is regarded as normal, yet polluting, the flow of uterine blood at an abnormal time is regarded as even more polluting. Is this because such a flow is regarded as a form of illness? But illness in itself is not polluting, for many serious forms of illness (e.g. bubonic plague) carry no charge of impurity at all. Certainly some of the sources of impurity are illnesses, notably ‘leprosy’, but most are not. Many people, contemplating the phenomena of ritual impurity, are irresistibly drawn to the view that the whole system is hygienic in inspiration, being designed to prevent the spread of disease by infection. The conveyance of impurity through touching or proximity in an enclosed area recalls modern ideas of germ-infection by contact or through the air. Certainly the idea of infectious disease was known in ancient times, especially in the form of plague. Yet this analogy breaks down at many points. The most we can say is that there is probably a hygienic component in the origins of the purity system. The system as we find it in operation in the Bible and rabbinic literature has no aim of preventing the spread of harmful infection, but merely of protecting holy areas and foods from desecration. No reasons are offered why these particular conditions or objects convey pollution to the holy, though we may speculate whether there is any basic concept uniting the various pollutions, or whether they are in fact a miscellaneous collection deriving from various historical milieux.

Childbirth is certainly a normal enough condition, even a highly prized one, yet it gives rise to an impurity that is greater than that of menstruation.