Chapter 2 of Mary Douglas's "Purity and Danger", titled "Secular Defilement" opens with a review of researchers', doctors and religious thinkers to account for "primitive" rituals and religious practices in terms of medical materialism, that is, as being a way of preserving public health. Douglas accepts the approach of medical materialism as long as it does not rule out other explanations, and she expands this notion to a general fear of all people of all cultures from violating ritualistic principles and the punish this might bring.
Douglas negated the distinction between "primitive" rituals and modern hygiene codes. She argues that symbolic system of defilement can be rather similar and the only difference is the way in which it is manifested in different cultures.
When reexamining the hygiene and defilement concepts of modern secular culture Douglas argues that what separates "primitive" defilement from secular defilement is that the secular avoids filth as a result of his knowledge in bacteriology and pathogens. However, Douglas holds that these principles still follow a perception of defilement as something which is not in its right place".
Douglas argues that there is an analogy between the concept of defilement and social order. What culture ascribes as defilement, profanity or impurity is something which is perceived as an anomaly and a break from the orderly boundaries of social and cultural order.
Douglas understands defilement as something which is culturally dependant and thus she rules out previous takes on the matter from a cultural evolution and hierarchy standpoint. A critique of Mary Douglas's notion of secular defilement might claim that her approach is too conservative, rigid and structuralist. Douglas's approach might be considered conservative in light of her relating to the social order as a self-evident and natural phenomenon as not as the result of social power relations that use the detentions of pure and impure, clean and unclean, to establish social hierarchies. Her rigid distinction between purity and defilement also does not allow for in-the-middle hybrid or liminal states. Another problem with Douglas's ideas in "Secular Defilement" is that she perceives culture as static and unchanging, and her theory isn't very productive when discussing social changes over time.
see also: Mary Douglas - Ritual Uncleanness