Head lice are tiny insects that live only on the scalp of human beings and are the size of a pinhead. They do not have wings so they cannot fly or jump, and they are not found on cats, dogs or any other household pets. The bites from head lice can cause itching and scratching. Scratching may cause sores which can get infected. Anyone can get head lice. School children get lice more than adults. When children play, their heads often touch. Lice crawl from head to head. Head lice can spread by direct head to head contact; however lice can live away from a human host for up to three days.
An infestation with lice is called pediculosis, and usually involves less than 10 live lice. Itching occurs if the individual becomes sensitized to antigenic components of louse saliva that is injected as the louse feeds. On the first infestation, sensitization commonly takes four to six weeks. However, some individuals remain asymptomatic and never itch. In cases with heavy infestations, secondary bacterial infection of the excoriated scalp may occur. Unlike body lice, head lice are not vectors for other diseases.
Based on the current medical research, it is essential that head lice be treated with two applications of an approved shampoo seven days apart. As long as the treatment has been administered properly, the presence of nits does not necessarily indicate an active infestation.