On an ordinary day some ten years ago, when I was in the midst of a long-forgotten project, a call came from preschool: “You need to pick up Andy. The nurse found head lice.” So began my first encounter with the horror, the shame, the benightedness—I had no idea then how common and manageable it could be—of this medieval infestation. I rushed over, and a solemn-faced nurse relinquished our child from his quarantine, along with an instruction sheet calculated to provoke alarm. Every article in the house was to be cleaned and deloused, every teddy bear, every curtain, every cushion, every sock. Andy’s head was to be scoured with a toxic shampoo whose perils to skin, eye and nervous system, advertised by many lines of small print, made me cringe. My husband was in California, leaving me to face all this alone.