Louse

A louse is a small, wingless parasitic insect in the order Phthiraptera that lives on the bodies of mammals or birds and feeds on skin or blood. In humans, the most common lice are species of Pediculus and Phthirus that infest the scalp, body, or pubic region.

In humans, three main types are recognized. The head louse, Pediculus humanus capitis, lives on the scalp and hair and feeds on blood. The body louse, Pediculus humanus corporis, spends most of its life on clothing and only visits the skin to feed. The pubic or crab louse, Phthirus pubis, infests coarse hair in the pubic region and adjacent areas. Lice are host-specific and do not jump between people; transmission occurs through direct contact or via infested items such as combs, hats, or clothing.

Lice go through a simple life cycle: eggs (nits) are laid on hair shafts or fabric fibers, hatch after about a week, and the immature nymphs molt three times before reaching adulthood. Adults live on the host, feeding regularly, with females laying numerous eggs over their lifespan. Off the host, head lice typically die within a couple of days, while body lice can survive longer when associated with clothing or bedding.

Symptoms commonly include itching and visible lice or nits on hair or clothing. Diagnosis is usually by finding lice or nits during careful inspection or combing. Treatment involves topical pediculicides, following product directions, and addressing contaminated items such as clothing and bedding. Close contacts may require screening or treatment in communal settings. Prevention focuses on avoiding sharing personal items and maintaining good hygiene. In historical contexts, body lice have been vectors for certain diseases, though such transmission is uncommon in modern, well-sited populations.