Head lice are parasitic insects that can be found on the head, eyebrows, and eyelashes of people. Head lice feed on human blood several time a day and live close to the human scalp, but are not known to spread disease.
Head lice are found throughout the world. In the United States, infestation with head lice is most common among preschool children attending child care, elementary school children, and the household members of infested children. It is estimated six to 12 million infestations occur each year in the United States among children three to 11 years of age.
Head-to-head contact with an already infested person is the most common way to get head lice. Head-to-head contact is common during play at school, at home, and elsewhere (sports activities, playground, slumber parties, camp).
Although uncommon, head lice can be spread by sharing clothing or belongings. This happens when lice crawl, or nits attached to shed hair hatch and get on the shared items recently worn or used by an infested person. People also can get head lice by lying on a bed, couch, pillow, or carpet that has recently been in contact with an infested person. Dogs, cats, and other pets do not play a role in the spread of head lice.
Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.
The diagnosis of a head lice infestation is best made by finding a live nymph or adult louse on the scalp or hair of a person. Because nymphs and adult lice are very small, move quickly, and avoid light, they can be difficult to find. Use of a magnifying lens and a fine-toothed comb may be helpful to find live lice.
Treat the infested person(s) requires using an over-the-counter (OTC) or prescription medication. Follow these treatment steps:
- Before applying treatment, it may be helpful to remove clothing that can become wet or stained during treatment.
- Apply lice medicine, according to the instructions contained in the box or printed on the label. If the infested person has very long hair (longer than shoulder length), it may be necessary to use a second bottle. Pay special attention to instructions on the label or in the box regarding how long the medication should be left on the hair and how it should be washed out.
- WARNING: Do not use a combination shampoo/conditioner, or conditioner before using lice medicine. Do not re-wash the hair for one to two days after the lice medicine is removed.
- Have the infested person put on clean clothing after treatment.
- If a few live lice are still found 8-12 hours after treatment, but are moving more slowly than before, do not retreat. The medicine may take longer to kill all the lice. Comb dead and any remaining live lice out of the hair using a fine-toothed nit comb.
- If, after 8-12 hours of treatment, no dead lice are found and lice seem as active as before, the medicine may not be working. Do not retreat until speaking with your health care provider; a different lice medicine may be necessary. If your health care provider recommends a different medicine, carefully follow the treatment instructions contained in the box or printed on the label.
- Nit (head lice egg) combs, often found in lice medicine packages, should be used to comb nits and lice from the hair shaft. Many flea combs made for cats and dogs are also effective.
- After each treatment, checking the hair and combing with a nit comb to remove nits and lice every two to three days may decrease the chance of self-reinfestation. Continue to check for two to three weeks to be sure all lice and nits are gone.
- Retreatment generally is recommended for most prescription and non-prescription (over-the-counter) drugs on day nine in order to kill any surviving hatched lice before they produce new eggs. However, if using the prescription drug malathion, which is ovicidal, retreatment is recommended after seven to nines days only if crawling bugs are found.
If you are not sure if a person has head lice, the diagnosis should be made by their health care provider, local health department, or other person trained to identify live head lice.