But why? What is it about toilet paper—specifically the prospect of an inadequate supply of it—that makes us so anxious? Some of the answer is obvious. Toilet paper has primal—even infantile—associations, connected with what is arguably the body’s least agreeable function in a way we’ve been taught from toddlerhood. Few, if any of us, remember a time when we weren’t acquainted with the product.

“There is comfort in knowing that it’s there,” says psychologist Mary Alvord, Associate Professor of Psychiatry and Behavioral Sciences at the George Washington University School of Medicine. “We all eat and we all sleep and we all poop. It’s a basic need to take care of ourselves.”

We are also exceedingly social creatures, and we count on the community for our survival. People seen as unclean or unwell are at risk of being shunned—which in the state of nature could mean death. “We’ve gone beyond using leaves,” says Alvord. “It’s about being clean and presentable and social and not smelling bad.”