Head Lice

What Is It?

Head lice are small, parasitic insects that infest hair on the head. Their six legs allow them to grasp individual hairs and wander between hairs. They feed only on the blood of people, and feed once or more each day.

A single insect is called a louse. A female louse can lay more than 100 eggs, called nits, in her lifetime. These eggs are attached to hairs close to the scalp by means of a very strong bonding material secreted by the female. They hatch about 8 days after they are laid, and grow to the adult stage about 9 to 12 days after hatching. Adult head lice survive just a few weeks.

In general, a person infested with head lice will have fewer than a dozen live lice on their head at a time, although hundreds of developing, dead and hatched eggs may be present.

Symptoms

The most common symptom of a head-lice infestation is itching. This is caused by the louse's saliva and feces, which irritates the skin on the scalp. The itching can be severe enough to prevent sleep, and some people scratch so much that they cause additional skin infections. Head lice are not known to transmit any infections.

Diagnosis

A medical professional should diagnose a head-lice infestation, and this should be based on the finding of a live (crawling) louse. Active lice infestations may be difficult to identify properly, since lice and their eggs are often hard to distinguish from other materials caught in the hair, such as dandruff, scabs, dirt or insects blown in by wind. A correct diagnosis is important because only active head-lice infestations should be treated. An infestation is considered active when live adult lice or developing eggs are observed. The eggs or nits of the louse appear as small white, tan or brown dots attached firmly to individual hairs close to the scalp. If nits are seen, then live lice should be sought before assuming the infestation is active.

Expected Duration

Head-lice infestations sometimes go away on their own because there are not enough insects to maintain the infestation, or they may persist for an indefinite period of time without treatment. With treatment, the infestation usually goes away in about two weeks.

Prevention

Head lice are acquired by direct contact with an infested person's hair. Only rarely would lice be transferred by shared combs, brushes, hats or other hair accessories.

Because direct head-to-head contact with an infested person is usually necessary to acquire head lice, it is not necessary to isolate infested people or keep children with head lice home from school.

Treatment

There are several treatment options that will likely succeed. In some cases, several methods can be used together to ensure success. First, make sure you have seen a live louse. Do not treat if you've only seen objects you believe to be louse eggs (nits). If you find a live louse on one person in the home, then inspect all other adults and children for lice as well.

If the hair can be combed easily, then you can use a special louse comb or nit comb to remove lice and their eggs from the hair. This sometimes requires combing several times a week until no lice are seen for two or more weeks. Although lice sometimes can be eliminated by combing, this method fails for some people. If the process requires too much time or causes discomfort, then it is not a good option for treatment.

Special insecticide products (pediculicides) are available in drug stores over the counter and by prescription. Do not apply any other kind of insecticide to the body or hair. Most pediculicides contain a class of chemicals called pyrethroids as the active ingredient. These usually are applied as a shampoo then washed off. A second treatment is often necessary, about 10 days later. Although these products work very well for many infestations, some head lice are resistant to them. If live (crawling) head lice are discovered a day after treatment, then you should speak with your doctor about other kinds of pediculicides that are available by prescription. Carefully read and follow the instructions on the product. Do not overtreat. If you have any questions about the use of the product, speak to your doctor or pharmacist.

Do not treat an active head-lice infestation with essential oils, enzyme treatments, antibiotics or suffocating agents such as oils, or heat. These treatments are either not known to be successful or may harm the person being treated.

Although lice are only rarely found on clothes, towels and bed linens, you may want to launder or change any items that have been in direct contact with the hair of the infested person. Washing items in hot water or drying them in high heat will kill lice and their eggs. Because head lice do not survive long once they are removed from a person, there is no need to clean or vacuum the home environment intensively.

When To Call A Professional

You should call your physician to confirm the presence of a head-lice infestation and to get help in determining how best to manage the problem. If you are unsure if the objects you see are lice or eggs, then you should have these examined before you treat.

Prognosis

The outlook for recovery from head-lice infestation is excellent. Head lice do not transmit other types of infections, nor do they produce symptoms other than itching. Active infestations that are treated according to directions will soon be eliminated.

Additional Info

Harvard School of Public Health

Laboratory of Public Health Entomology

Department of Immunology and Infectious Diseases

665 Huntington Ave.

Boston, MA 02115-6021

http://www.hsph.harvard.edu/headlice.html