With Manders’s cartoon illustrations adding detail and lighthearted commentary, Lauber revisits sanitary facilities down the ages, as well as common attitudes toward them. After a speculative glance into prehistory, she traces the development of public and private baths from the Indus River Valley to the early 20th century, focusing largely on Europe but pausing to mention early steam baths in the Americas, along with certain Muslim and Hindu practices. Children will come away with a clearer understanding of how standards of cleanliness can vary—from culture to culture, as well as era to era—plus just a few grossout facts suitable for sharing with siblings and parents, such as the sponge dipped in salt water that ancient Romans used in lieu of toilet paper. This follow-up to What You Never Knew About Fingers, Forks, and Chopsticks (1999) invites repeated dips. (Nonfiction. 7-9)