Children have returned to school and are bringing home stories about the things they learned and the friends they made. But some parents are concerned they could also be bringing home a tiny nuisance: head lice.

The parasitic insects are about the size of a sesame seed and feed on human blood, usually living on a person's scalp, according to the Centers for Disease Control and Prevention .

While schools are not the only place people can get them, the CDC says head lice infestations in the U.S. are most common among preschool and elementary-age children. The U.S. sees up to 12 million head lice infestations annually in children between 3 and 11 years old, according to the health agency.

Lice cannot hop, jump or fly. The most common way to get them is through head-to-head contact wit

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