Pediculosis capitis, the head louse, is one of humanity's constant-and unwelcome-companions. It has become adapted to a narrow environmental niche-living as a parasite on the human scalp. Related forms of louse have adapted to living as parasites on the body (body louse) or on the pubic area (crab louse).
The bite of a louse is usually undetectable, but the site of the bite becomes inflamed and itchy. The most common first symptom of infestation with head lice is intense itching. Examination of the scalp will reveal red, swollen patches in the itchy areas. Examination of the hair typically reveals clusters of grayish-white louse eggs (nits) attached to the hair shafts. Further examination will usually find live adult lice.
Outbreaks of head louse infestation are most likely at sites such as schools, nursing homes and military barracks where people come into close contact. A head louse infestation does not necessarily indicate that the infested person is "dirty", although this is a common belief. An infestation simply indicates that a person came into a situation where transfer of lice or louse eggs could easily occur.
Once a head louse infestation has been discovered, all members of the household or community (nursing home, barracks) should be examined. Consideration may be given to treating the entire household or community with anti-louse medication. All clothing should be thoroughly washed in very hot water, or dry cleaned. All combs and brushes should be cleaned and washed in anti-louse medication. Over-the-counter anti-louse medications are available and may be adequate to bring a single infestation under control when properly used. More potent oral and topical anti-louse medications are available only by prescription.