Lice are tiny, wingless insects that live on the skin of humans and animals, feeding on blood. Each louse (that's the singular form) is about the size of a sesame seed, and while they can't fly or jump, they crawl quickly and spread easily when people share hats, brushes, or touch heads together.

The most common type kids encounter is head lice, which live in human hair. Having lice doesn't mean someone is dirty: these parasites can affect anyone. They cause itching because their bites irritate the skin. While annoying and uncomfortable, lice usually don't spread disease.

Getting rid of lice requires careful work: special shampoos kill the bugs, but you also need to comb out their eggs (called nits), which stick stubbornly to hair shafts. Schools sometimes send notes home warning about lice outbreaks so families can check their children.

Other animals get their own species of lice too. Body lice affect humans differently than head lice, and throughout history, lice infestations have plagued armies, prisons, and crowded places where people couldn't bathe regularly. Today, lice remain one of childhood's most common nuisances, though they're treatable with patience and the right approach.