The Associated Press writes in this story that some schools in a number of states have relaxed the rules, allowing students with lice to stay in class. The reason? School officials figure that kids actually are contagious well before anyone realizes they have lice, so the damage has already been done. In fact, the American Association of Pediatrics and the National Association of School Nurses advocate that schools don’t force kids with lice to stay home.

Lice, if you’ve been fortunate enough to escape it, are very small grayish-white parasitic insects that can live on people’s heads and bodies. Schools often deal with outbreaks of head lice, which usually spread by close person-to-person contact. (This is why moms tell their children not to use someone else’s brush or wear someone else’s hat.) Lice attach themselves to the scalp and neck and attach eggs to the base of the hair shaft. They crawl rather than fly. Lice aren’t a health hazard, and their appearance has nothing to do with hygiene, but they are itchy and, well, revolting, and getting rid of them isn’t easy.