Find out how these tiny insects that feed on blood from the human scalp can spread from person to person, along with treatment options.
Head lice are tiny insects that feed on blood from the human scalp. Head lice most often affect children. The insects usually spread through direct transfer from the hair of one person to the hair of another.
Having head lice isn't a sign of poor personal hygiene or an unclean living environment. Head lice don't carry bacterial or viral diseases.
Nonprescription and prescription medications can help treat head lice. Follow treatment instructions carefully to rid the scalp and hair of lice and their eggs.
People also use a number of home or natural remedies to get rid of head lice. But there is little to no clinical evidence that they're effective.
Head lice feed on blood from the scalp. The female louse lays eggs (nits) that stick to hair shafts.
Common signs and symptoms of head lice may include:
See a health care provider before you begin treatment if you suspect that you or your child has head lice. Your or your child's health care provider can confirm that head lice are present. Studies show that many children have been treated for head lice with nonprescription medications or home remedies when they didn't have lice.
Things often mistaken for nits include:
A head louse is a tan or grayish insect about the size of a strawberry seed. It feeds on human blood from the scalp. The female louse produces a sticky substance that firmly attaches each egg to the base of a hair shaft less than 1/4 inch (5 millimeters) from the scalp.
A louse goes through three stages:
Head lice crawl, but they can't jump or fly. Head lice often spread from one person to another by direct head-to-head contact, often within a family or among children who have close contact at school or play.
It's less common for head lice to spread without direct contact. But the insects may spread from one person to another through personal items, such as:
Head lice may also spread when items of clothing are stored together. For example, hats or scarves hung on the same hook or stored in the same school locker could serve as vehicles for spreading lice.
Household pets, such as dogs and cats, don't play a role in spreading head lice.
Head lice are spread primarily by direct head-to-head contact. So the risk of spreading head lice is greatest among children who play or go to school together. In the United States, cases of head lice most often occur in children in preschool through elementary school.
If your child scratches an itchy scalp due to head lice, it's possible for the skin to break and develop an infection.
It's difficult to prevent the spread of head lice among children in child care facilities and schools because there is so much close contact.
The chance of indirect spread from personal items is slight. However, to help prevent head lice from spreading, you may tell your child to:
It's not necessary to avoid sharing protective headgear for sports and bicycling when sharing is required.
According to the American Academy of Pediatrics guidelines, the gold standard for diagnosing head lice is to identify a live nymph or adult louse.
The guidelines recommend examining wet hair lubricated with hair conditioner or another product. Your child's health care provider will carefully comb your child's hair with a fine-toothed comb (nit comb) from the scalp to the end of the hair. If no live louse is found, the provider will likely repeat the entire exam at a second appointment.
Your health care provider will also look for nits in your child's hair. To find nits, your child's provider may use a specialized light called a Wood's light, which causes nits to appear bluish. But the identification of nits does not necessarily confirm the diagnosis of live lice.
A live nit needs to be near the scalp to survive. Nits found more than about 1/4 inch (6 millimeters) from the scalp are likely dead or empty. Suspect nits can be examined under a microscope to determine if they're living.
If the provider doesn't find any live nits, they're probably left from a previous case of head lice and don't need to be treated.
Your health care provider will likely recommend a medication available without a prescription that kills lice and some of the nits. These medications may not kill recently laid eggs. Therefore, an appropriately timed second treatment is usually necessary to kill nymphs after they hatch but before they become adult lice.
Some studies suggest that re-treating 7 to 9 days after the first treatment is the ideal time for a second treatment, but other re-treatment schedules exist. Ask your health care provider for written instructions for a recommended treatment schedule.
Medications available without a prescription include:
Permethrin (Nix). Permethrin is a synthetic version of pyrethrin, which is a chemical compound extracted from the chrysanthemum flower. Permethrin is toxic to lice.
Before using permethrin, wash your child's hair with shampoo but not conditioner. Rinsing the hair with white vinegar before washing may help dissolve the glue that holds the nits to the hair shafts. Leave the medication in the hair for the amount of time indicated in the directions on the package. Then rinse your child's hair over a sink with warm water.
Permethrin doesn't kill nits, and treatment needs to be repeated 9 to 10 days after first application. Side effects may include redness and itching of the scalp.
In some regions, lice have developed resistance to nonprescription medications. Nonprescription treatment also may fail because of incorrect use, such as not repeating the treatment at an appropriate time.
If the correct use of a nonprescription treatment has failed, your health care provider may recommend a prescription treatment. These include:
If you prefer not to use a medication for treating head lice, you may consider a home treatment. However, there's little to no clinical evidence that home treatments are effective.
Combing wet hair with a fine-toothed nit comb may remove lice and some nits. Studies show that wet-combing results vary.
Start by wetting the hair and lubricating it with hair conditioner or olive oil. Comb the entire head from the scalp to the end of the hair at least twice during a session. The process typically should be repeated every 3 to 4 days for several weeks — at least two weeks after no more lice are found.
Small clinical studies have suggested that some natural plant oils may kill lice by depriving them of air, but effectiveness is uncertain. These products include:
Essential oils aren't required to meet safety, efficacy and manufacturing standards used for drugs approved by the Food and Drug Administration (FDA), and can sometimes cause allergic reactions.
A number of household products are used to treat head lice. These products are thought to deprive the lice of air when generous amounts are applied to the hair, covered with a shower cap and left on overnight. Products used for this purpose include:
However, it's unclear if these treatments are effective.
Another option is a machine that uses one application of hot air to kill head lice and their eggs through dehydration. The machine requires special training and is currently available only at professional lice treatment centers.
The machine uses air that is cooler than most hair dryers and at a much higher flow rate to kill the lice by drying them out. Don't use a regular hair dryer to accomplish this result as it's too hot and could burn the scalp.
Flammable products, such as kerosene or gasoline, should never be used to kill lice or to remove nits.
Lice usually don't live past one day without feeding from a human scalp. And eggs can't survive without the temperature near the scalp. Therefore, the chance of lice surviving on household items is small.
As a precaution, you may clean items that the affected person has used in the previous two days. Cleaning recommendations include the following:
See your family's health care provider or pediatrician if you suspect that your child has head lice. The provider will examine your child's scalp and look for a live nymph or adult louse to determine if he or she has head lice. The provider can carefully inspect your child's hair. If necessary, the provider can examine suspect items under a microscope before confirming that head lice are present.