Head lice are parasitic insects that can be found most commonly on the scalp, particularly around and behind the ears and near the neckline at the back of the head. They are less commonly found on the eyebrows or eyelashes of people. Head lice feed on human blood several times a day. They live close to the human scalp. Head lice are not known to spread disease.
Head lice have three forms: the egg (also called a nit), the nymph, and adult. Nits are laid by the adult female at the base of the hair shaft nearest the scalp. They are firmly attached to the hair shaft and are very small. Nits are often confused with dandruff, scabs, hair spray droplets or dirt particles. Head lice nits usually take 8 to 9 days to hatch. A nymph is an immature louse that hatches from the egg. A nymph looks like an adult head louse but is much smaller. A nymph must feed on blood to live. Nymphs mature into adults after 9 to 12 days from hatching. An adult louse is about the size of a sesame seed, has six legs, and is tan to grayish-white in color. They too must feed on blood to live. An adult can live about 30 days on a person’s head but will die within 1 or 2 days if it falls off. Adult female head lice are usually larger than males.
Signs and symptoms of head lice infestation are:
- Tickling feeling of something moving in the hair.
- Itching caused by an allergic reaction to the bites of lice.
- Irritability and difficulty sleeping as head lice are more active in the dark.
- Sores on the head caused by scratching. These sores can sometimes become infected from bacteria on the person’s skin.
Head lice are found worldwide. In the United States, head lice are most common among pre-school children attending child care, elementary schoolchildren, and the household members of infested children. An estimated 6 million to 12 million infestations occur each year in the United States among children 3 to 11 years of age. In the United States, infestation with head lice is much less common among African-Americans than among persons of other races.
Head lice move by crawling; they cannot hop or fly. Head lice are spread by direct contact with the hair of an infested person. Anyone who comes in head-to-head contact with someone who already has head lice is at greatest risk. Spread by contact with clothing (such as hats, scarves or coats) or other personal items (such as combs, brushes or towels) used by an infested person is uncommon. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice. Dogs, cats, and other pets do not have a role in the spread of head lice.
Head lice should not be considered as a medical or public health hazard. Head lice are not known to spread disease. Head lice can cause a tickling feeling or a sensation of something moving in the hair. Head lice can be an annoyance because their presence may cause itching and loss of sleep. Sometimes the itching can lead to excessive scratching that can sometimes increase the chance of a secondary skin infection.
According to the Centers for Disease Control and Prevention (CDC), students diagnosed with live head lice do not need to be sent home early from school; they can go home at the end of the day, be treated, and return to class after appropriate treatment has begun. Nits may persist after treatment, but successful treatment should kill crawling lice.
Head lice can be a nuisance but they have not been shown to spread disease. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.
Both the American Academy of Pediatrics (AAP) and the National Association of School Nurses (NASN) advocate that “no-nit” policies should be discontinued. “No-nit” policies that require a child to be free of nits before they can return to schools should be discontinued for the following reasons:
- Many nits are more than ¼ inch from the scalp. Such nits are usually not viable and very unlikely to hatch to become crawling lice, or may in fact be empty shells, also known as ‘casings’.
- Nits are cemented to hair shafts and are very unlikely to be transferred successfully to other people.
- The burden of unnecessary absenteeism to the students, families and communities far outweighs the risks associated with head lice. Students miss learning opportunities when burdened by over-cautious school policies.
- Misdiagnosis of nits is very common during nit checks conducted by non-medical personnel.