Controlling Head Lice

Gene R. Strother - Extension Entomologist

Head Louse on Human HairHead lice are a common problem that can affect anyone, regardless of age or personal habits. However, they are most common in school-age children. This publication contains answers to some of the most commonly asked questions about head lice.

What are head lice, and what do they look like?

Head lice are small, flat insects; the adults are about 1/8 inch in length. They have no wings, and they do not fly or jump. Their color varies from a dirty white to grayish black. Head lice have sucking mouthparts and suck blood. They live on the head and spend their entire life cycle in the hair. They have six legs and relatively large claws for grasping and holding on to human hair. They crawl through the hair.

How does a person get head lice, and how are they spread?

Life Cycle of Head LouseMost commonly head lice are spread from an infected person to an uninfected person by direct contact with the hair, as when children hug and play. They are also spread by sharing personal items such as brushes, combs, towels, hats, caps, and head gear. Sharing lockers and coat racks at school has been associated with the spread of head lice.

Lice may leave the head when there is physical contact with another head, when they are displaced by combing or brushing, or when they are removed with hats or other head gear.

A head louse infestation is often a group, family, or classroom problem. If one person who has intimate contact with a group of people gets infested, the infestation may quickly spread to others in the group.

Communal sharing of combs and brushes, participation in contact sports, and sharing of training head gear are some of the most common ways head lice are spread.

How do head lice live, and how fast do they multiply?

The adult female head louse lays her eggs (nits) at the base of the hair near the scalp. The eggs hatch in about 8 or 9 days. The newly hatched louse (nymph) will suck blood for food and shed its skin (molt) three times as it develops into an adult over a 10-day period. The young lice and adults live their entire lives on the head, feeding on blood. The entire life cycle takes about 3 weeks.

Head lice are completely dependent on human heads for warmth and food. They need about five blood meals each day and lay six to eight eggs a day. The eggs are glued to the hair shaft very close to the scalp. Head lice live only about 30 to 40 days. They die in 1 or 2 days when removed from the head, and eggs die soon after being removed from the warm scalp. Head lice do not wander about rugs, furniture, or school buses seeking a host.

Do only certain types of people get head lice?

There are no social or economic barriers to the head louse. Lice do not pick or choose clean or dirty heads. They are more commonly found on children 3 to 12 years old and become progressively less common as children grow older. However, they readily live on adults and people of any age if given the opportunity. Close contact during play and a lack of awareness as to why their heads itch make young children more susceptible to head lice.

African-American children get head lice much less frequently than children of other backgrounds do, apparently because of a difference in the structure of the hair shaft.

What do you look for when checking for head lice?

Living adults and nymphs are signs of an active infestation. Both can move quickly and shy away from light, making them difficult to see. The eggs are easier to see than the adults. Eggs are most commonly found at the back of the neck, behind the ears, and at the crown of the head. When eggs are first deposited, they are glued to the hair shaft near the scalp. As the hair grows, however, the attached egg is moved farther and farther from the scalp, providing a general indication of the length of time since the original infestation occurred.

Itching and skin irritation at feeding sites are associated with head lice. In children, head lice may cause inattention in school and loss of sleep because of the itching. Skin irritation may take several weeks to develop, so newly infested people may not be aware that they have head lice.

Dark fecal spots on pillow cases and on light colored collars can indicate the presence of head lice. If these dark spots are found, check the head to confirm the presence of lice.

Sometimes debris or hair oil can be mistaken for lice eggs. Since the egg is firmly glued to the hair shaft, any debris or spot that moves easily up and down the hair is not an egg.

How do you get rid of head lice?

When head lice are found, all members of the family should be examined. Only those showing evidence of infestation should be treated. Infested persons in the family should all be treated at the same time to prevent reinfestation from one family member to another.

Three different insecticides are labeled for head lice control and are available at most drug stores:

Natural pyrethrin formulations, which are sold under a number of labels, are effective but have very little residual activity. The synthetic pyrethroid permethrin (Nix) is effective and has a 10-day to 2-week residual effect after application. Both the natural pyrethrins and Nix may be purchased over the counter at most drug stores. Lindane (Kwell) is effective but is sold only with a prescription. Kwell takes longer to kill adults and nymphs than the other insecticides.

Treatment usually involves wetting the hair with the insecticide formulation, allowing it to remain a certain length of time, and then shampooing it out. Be sure to follow label instructions and use only products labeled for head louse control.

Remove clothing from the upper body before treatment, and use a towel to protect the eyes. Confine the treatment to the scalp and neck, and administer it over a sink-not in a shower or bathtub.

Consult your physician before treating anyone who has extensive scratches or cuts on the head or neck or anyone who is ill or using medications. Lice or nits in the eyebrows or eyelashes, on an infant, or on pregnant women should be removed by hand. Do not use an insecticide in the eye area.

Despite certain manufacturers' claims, neither Kwell nor various over-the-counter pyrethrin formulations will kill all the eggs in the hair. When using Kwell or the pyrethrins, a second treatment is essen tial to kill young lice hatching from eggs not killed in the first treatment. However, studies show that 98 to 99.6 percent of subjects treated with a single treatment of Nix were louse-free after 14 days. Nix leaves a residue in the hair that protects against reinfestation for up to 2 weeks.

Should eggs (nits) removed?

Authorities in school systems, recognizing that some insecticides do not kill every egg, often require that all eggs (nits) be removed from a child's head after treatment before the child is allowed back in school. This "no-nit policy" reduces exposure to an insecticide (with one treatment rather than two). It also makes reinspection of returning children easier for school and health authorities, because they don't have to distinguish between live and dead eggs. Dead nits and empty egg shells remain glued to the hair shaft and can create the appearance of reinfestation.

Nits can be removed with a special lice comb often included with an insecticide treatment kit. They can also be removed with fingernails or cut out with small scissors. Nit combing is easier when the hair is damp. Some nit combs have teeth too far apart to be very effective. When small children have been treated, parents should make a daily inspection for at least 10 days after the initial treatment and nit removal. Retreatment is necessary if nits or lice are found during this period.

Can you still have lice after you have been treated?

Several factors may make a louse control treatment unsuccessful:

Remember that head lice are a community problem. Treating an individual without inspecting (and treating, if necessary) classmates, close friends, or relatives is likely to cause reinfestation. The whole group close to the infested person should be inspected. In the case of a school, the inspection should be done by trained school personnel or by county health personnel so that everyone infested can be treated at the same time. Regular inspections using a "no-nit policy" will ensure that there are no reinfestations.

Should the home or school be treated if head lice are found?

There is no evidence that applying insecticides to rugs, floors, furniture, classrooms, or school buses has any benefit in head lice control. These sprays often cause unnecessary exposure to insecticides.

Most experts on louse control recommend following these extra steps at the time of the first treatment:

  1. After removing nits, change clothing and bed linen.
  2. Machine-wash hats, scarves, and bed linen at 140 degrees F or dry them at high heat for at least 20 minutes. Dry-clean clothing that is not machine-washable.
  3. Soak combs and brushes for 1 hour in a 2-percent Lysol solution or put them in a pan of water heated to 150 degrees F for 5 to 10 minutes.
  4. As an added precaution, vacuum chairs and lounging areas used by the infested person.

What can I do to prevent head lice in my family?

When you hear of head lice in your community, check the heads of family members daily for evidence of lice for at least 10 days.

Discourage the sharing of combs, brushes, hats, and other head gear. Discourage small children from hugging or engaging in other activities in which their heads or hair comes into direct contact.

Encourage daily brushing and combing of hair. Lice do not like disturbances and will grip surround ing hairs with all six legs to avoid being removed. If a comb or brush darnages the louse, it will die. Combing and brushing the hair can be a good preventive measure.

Cooperate with your county health or school officials by following the control strategy they recommend. Treating only one child in an infested group will usually result in the child's becoming reinfested.

Remember, it is no disgrace to have head lice. If a member of your family gets head lice (especially small children), let everyone with whom the person has had close contact know of the infestation. These people should be checked for head lice, too. The greatest friends head lice have are people who fear the social stigma and treat their head lice secretly.