This Chapter, published by Depends on timing. the journal Asian Ethnology, is a theoretical exercise, inspired by Mary Douglas’s classic anthropological text Purity and Danger, that sets out to clarify the wide range of relationships between religions and humanitarian traditions as ideological movements, taking Islam as an instance. It postulates that the concept of the “sacred” is a special case of boundary maintenance or “purism”. Metaphorically, “puripetal force” (a neologism) is defined as a tendency common to all ideological systems, a resistance to social entropy or anomie. An explanatory model is proposed that accommodates forms of concentrated purism such as (within Islam) Wahhabi-Salafism and (within humanitarianism) the legacy of Henry Dunant, founder of the International Committee of the Red Cross. Specific Islamic charities and welfare organizations interact differentially with both religious and humanitarian traditions. Meanwhile, US government policy towards charities sometimes seems dominated by an urge to peer into purity of motives. Finally, it is suggested that the model could equally be applied to Christian and other religious traditions, with the concluding thought that the common ground between the institutions of international humanitarianism and religious traditions is currently expanding.