Head lice can't form colonies in carpet or anywhere else in a home, Guillebeau said. They require a human host to spread an infestation and can "live off the body no more than a day or two."

Unlabeled treatments, such as kerosene and yard chemicals, applied to a child's head can be dangerous. And medicated head lice shampoos won't kill all the eggs, known as nits, Pettis said.

The only way to get rid of head lice completely is with a combination of the shampoos and manual removal. To remove the nits, a parent or guardian must comb through each section of a child's hair from the root all the way to the tip.

"The quality of a nit comb makes a big difference," Guillebeau said. "The best are made out of steel. Inexpensive plastic combs are just not as good."

When parents use a nit comb, Pettis said it's best to dip the comb in warm, soapy water after each sweep through the child's hair.

"The biggest take-home message to parents is to encourage schools not to spray pesticides," she said. "Sprays expose children to unnecessary risks and aren't effective for head lice management. And always use a nit comb. It's an essential part of lice removal."

- Stephanie Schupska