I remember it well: our dark winter of itch when the kids were small. It started with a note sent home—years before the pandemic—that my child had been exposed, not to a deadly virus but to lice.

Ever had an itch you can't scratch? Maybe it's out of reach, or your hands are full, or you don't want to damage your skin. It can be deeply frustrating. And even though the itch response, or what ...