ST. LOUIS (AP) — A study that suggests a new strain of lice may be resistant to typical treatments comes as children are headed back to school, and some districts have loosened their attendance policies over students with the bugs.

The St. Louis Post-Dispatch reports that health experts say head lice aren’t a sign of poor habits, as the tiny pests prefer clean hair. But those who work at Lice Busters say the social stigma attached to the lice remains, that only those living in dirty homes get infestations.

A sample policy for districts by the Missouri School Boards’ Association says a student found with live head lice shouldn’t return to school for 24 hours to allow for treatment. But it says districts shouldn’t exclude otherwise healthy students from school if only eggs are found.