Head lice are small flat, wingless, bloodsucking insects that live almost exclusively on hairs on the human head. One individual insect is called a head louse. Mature females lay tiny, pearly eggs called nits that they “glue” firmly to the base of individual hairs. Both adult lice and nits can be detected by careful inspection, but they are not easy to see. Head lice rarely transmit diseases. But their bites can cause discomfort and intense itching, and people find their presence alarming.
Head lice usually spread from one person to another by direct head-to-head contact. Sometimes, the lice may travel on hairbrushes, hats, scarves, or other objects. Infestation can happen to anyone, but it is more common among young children than among teen-agers or adults. Getting head lice has no relationship to cleanliness, wealth, or the texture or other characteristics of hair.
Some reports suggest that the number of cases of head lice has increased since the 1970’s. Many experts think that an increase may have occurred because the lice developed resistance to chemicals in shampoos and rinses commonly used to kill them. Infestations can also be reduced or eliminated by nit-picking—that is, physically removing adults and nits by hand or with special fine-toothed combs.
