Head lice are tiny insects that live on the human scalp and feed on blood. They're about the size of a sesame seed when fully grown. Contrary to popular belief, lice don't discriminate — they can live in all types of hair regardless of length, texture, or cleanliness. Lice crawl, they don't fly or jump. They spread primarily through direct head-to-head contact, which is why they're common among children who play closely together. They can also spread through sharing items that have been in contact with the head like hats, combs, or pillows.