Disgust has deep psychological roots, emerging early in a child’s development. Infants and young toddlers don’t feel grossed out by anything—diapers, Rozin observes, are there in part to stop a baby “from eating her shit.” In the young mind, curiosity and exploration often overpower any competing instincts. But, at around four years old, there seems to be a profound shift. Suddenly, children won’t touch things that they find appalling. Some substances, especially human excretions of any sort, are seen as gross and untouchable all over the world; others are culturally determined. But, whether universal or culturally-specific, the disgust reactions that we acquire as children stay with us throughout our lives. If anything, they grow stronger—and more consequential—with age.
—Maria Konnikova, writing in The New Yorker about the cultural dimensions of disgust, and how our emotions can get in the way of public health advances—specifically in the context of recycled water.