Purity and Danger: An Analysis of the Concepts of Pollution and Taboo is a classic book by British anthropologist Mary Douglas, and is considered one of the most important works in anthropological literature in the 20th century.
For a short version see Purity and Danger - short summary
"Purity and Danger" deals with impurity and dirt from an anthropological point of view and includes an analysis of rituals, religiosity and lifestyles that challenge, according to Douglas, Western perceptions of pollution, while trying to show how these perceptions are understood from a cultural and historical context. At the heart of the book is Douglas' question: Why do cultures attach certain importance to certain things, while other things are considered so polluted that they are taboo? In an attempt to answer this question, Douglas traces the laws of impurity and purity of Zaire tribes while comparing them to Jewish laws of kashrut in the Book of Leviticus. Douglas' main argument in the book is that what counts as dirt in a given society is everything that is considered out of place (food is not dirty by nature, but food stains on clothes are considered dirt; dirt is not dirty unless it enters the house and so on.
One of the main ideas of “Purity and Danger” is " Secular Defilement", according to which modern hygiene practices are not structurally different from the "primitive" ones. In "Purity and Danger" Mary Douglas first proposed the idea that the kosher laws of the Jews were not primitive health regulations as is commonly thought or arbitrary rules expressing the Jews' commitment to God. Instead, Douglas argued that kosher rules reinforce symbolic boundaries of Jewish culture. Kashruth laws are in fact part of the system of diagnoses and symbols that Jewish society has created to distinguish between the underlying categories, such as purity-impurity, good-evil; The exceptions are the unclean. Prohibited foods according to Halacha (Jewish law) were those that did not fit into any defined category. For example, the place of pigs in the natural order is not unequivocal because they are hoofed but not live, so they "break" the sorting criterion. Douglas therefore concludes that impurity is an expression of anomaly and disorder, and one of the ways to deal with unusual phenomena that cause a person noticeable discomfort is through the removal of the anomalous object and its definition as unclean.
Douglas tries to clarify the differences between holy, unclean and defiled in different cultures and times in the world. To understand impurity she takes a structuralist approach, following in the footsteps of Emil Durkheim and Claude Levy-Strauss who have explored culture as a system that reflects the universal nature of human thinking. Douglas states that impurity is the result of transgressing the boundaries of order, going beyond the boundaries of sociocultural organization. Another distinction found in “Purity and Danger” is the connection between the personal dimension and the public-political dimension. According to her, rituals that express anxiety about the body's perforations - blood, pus, semen, etc. - stem from the desire to protect the political and social unity of a minority group. According to her, the Jews' concern for the integrity of the physical body reflects the threat they felt to their bodies.
According to Douglas, modern perception is not pollution-oriented (at most pollution is perceived as a matter of aesthetics, hygiene or ethics and the only problem it can create is discomfort). In contrast to tribal perceptions among tribes where there is no “differentiation” and everything is one percent in another, the infection is perceived as a sin.