CHICAGO (AP) - A common school policy for preventing head lice infestations is probably too restrictive, needlessly excluding many non-contagious children from class, government research suggests.

At issue are nits - the egg casings for the tiny, itchy, bloodsucking insects. Lice are generally harmless but contagious, and many schools have adopted ``no-nit'' policies barring youngsters with nits even when there is no evidence of lice.

Nits resemble tiny white grains and may contain developing lice. But some are simply empty shells. They often remain attached to hair long after adequate treatment, according to the study by researchers at the Centers for Disease Control and Prevention.

``Most children with nits alone will not become infested,'' the authors wrote in the May issue of the journal Pediatrics.

Special shampoos or lotions containing insecticides can treat head lice, which infect an estimated 6 million to 12 million U.S. children annually.

The study involved children at two Atlanta-area elementary schools; 28 had lice and 50 had just nits. Just nine of the nits-only children developed lice during a two-week follow-up.

The authors suggest that instead of being excluded from class, children with just nits could undergo brief scalp exams at school to make sure they have no lice.

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