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They are miniscule, measuring at most 2 mm to 3 mm long, yet few things induce more panic or fear among parents than head lice. But while an infestation of head lice on a child can be uncomfortable, the critters do not pose enough of a contagious hazard to justify the strict policies that many schools use to keep infected children out of class, according to a new report from the American Academy of Pediatrics (AAP).

In the clinical report, released by the journal Pediatrics on Monday, the AAP updates its 2002 guidelines for the treatment of lice infestation. The pediatricians group once again urges schools to abandon their strict no-nits policies, which require children to be free of nits, the empty casings left behind by lice once they hatch from their eggs, before they may return to school. Both the AAP and the National Association of School Nurses have long discouraged this policy because it is not proven to lower overall infestation rates and puts children who miss class at a disadvantage. "We are trying to take a firmer position against the no-nits policy because it makes no medical sense and was never shown to be effective," says Dr. Barbara Frankowski, a pediatrician at Vermont Children's Hospital and past chair of the AAP's Council on School Health, which authored the new report.

Frankowski adds that parents wrongly tend to blame schools for the spread of head lice. "Parents have the idea that lice comes from schools and that it's the school's job to get rid of it, when in actual fact a lot of head lice comes from situations where kids are in close contact, such as sleepovers and camps," she says.

Head lice is not a reportable disease, so school and health officials cannot calculate the exact number of cases among school-age children. However, based on extrapolations from documented local infestations, estimates range from 6 million to 12 million cases in the U.S. each year — figures that have not declined significantly since the AAP's last report in 2002, despite schools' no-nits policies, Frankowski says.

Richard Pollack, a research associate at the Harvard School of Public Health who did a study of tens of thousands of children about a decade ago, reported that schools with no-nits policies showed no fewer cases of lice than those without the policies. He also found that nearly half of the cases that parents, nurses and other school volunteers had diagnosed as head lice were nothing but debris or dandruff in the hair. "The vast majority of children who were sent home from school because of the presumption of lice were misidentified or misdiagnosed," he says.

That is why the AAP is taking a stronger position against head-lice policies that keep children out of school. The new report — which begins its recommendations by affirming that "no healthy child should be excluded from or allowed to miss school time because of head lice" — further advocates keeping children in school even if they have a lice infestation, provided that the child is being treated properly. The report offers parents and pediatricians more detailed information than previous guidelines on which treatments to use, particularly when the first-line remedy — over-the-counter shampoos containing permethrin — is not effective.

The AAP is hoping to increase pediatrician involvement in treatment decisions, since second-line therapies, including malathion and benzyl-alcohol solutions, require prescriptions, Frankowski says. A physician's oversight may also help lessen the problem of treatment resistance to permethrin because doctors are trained to distinguish between adult lice and eggs. In many cases, parents assume treatment has not worked if they continue to see lice after the first or second application of permethrin. But what may be happening is that permethrin dispatches adult lice but not their eggs — no therapy is 100% effective at killing lice eggs — so the presence of baby lice that hatch seven to 14 days after treatment gives parents the false impression that the lice are resistant.

Frankowski hopes that the AAP's new statement will encourage parents and school boards to base treatment decisions on scientific evidence and keep them from reacting emotionally to infestations. "We in the U.S. have a bug phobia," she says. "But it's only against the bugs we can see." She points out that microscopic dust mites, which live in beds in nearly every household and feed on shed human skin, should be just as disturbing to people as lice, but because they are out of sight they tend to remain out of mind.

Indeed, the growing medical evidence appears to be helping more school districts ease up on restrictive return-to-school policies. Increasingly over the past year, school boards across the country have accepted that lice do not represent enough of a public health threat to keep children at home and have abandoned their no-nits policies, according to Martha Bergren, director of research for the National Association of School Nurses. "What we are seeing is much less resistance to changing the policy, and the tide is turning," she says.

The Oakland Unified School District in Southern California, for example, did away with its lice policy altogether, arguing that if there is no evidence that having strict criteria for checking for lice and controlling infestations in children does any good, then there is no need for a policy. In New York City, public schools took a more stepwise approach in 2007, moving from a no-nits policy to a no-head-lice policy that requires children not to show any signs of active live-louse infestation before returning to school. "New York City made a baby step," says Harvard's Pollack, who consulted with health officials there. "I would love to have seen them do away with the policy completely, but at least they made a step in the right direction. Maybe this AAP report will help them make another step in the right direction and remove the policy altogether."

• Alice Park
• The medical evidence suggests that schools' no-nits policies, which keep children out of class, do little to reduce head-lice infestations