Lice come from other infected people. Head lice, for example, are tiny parasitic insects that live on human scalps and are spread almost exclusively through direct head-to-head contact with someone who already has lice. While there is a slight possibility of transmission via shared items like brushes or hats, nearly all cases are due to close contact. Lice have evolved alongside humans for millions of years, with head lice specifically adapting to live on the scalp while body lice adapted to clothing. Humans get lice when live lice or their eggs (nits) are transferred from one person to another. Female lice lay eggs attached firmly to hair strands close to the scalp, and these hatch into nymphs before becoming adults, continuing the cycle. Lice cannot survive long away from a human host, typically only hours to a day outside the scalp. The presence of lice is ancient, with evidence suggesting lice have existed for over a million years, evolving alongside human development such as clothing use. Different genetic types (clades) of head lice have geographic origins in different parts of the world, like North America and Europe. In summary, lice come from other infested humans through close contact, and they have a long evolutionary history tied to humans and their habits like clothing use.