Head Lice


What Is It?

Head lice are small, parasitic insects that infest hair on the head. They have six legs and can grasp individual hairs. They feed on blood once or more each day and live two to three weeks.

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 eight days after they are laid. Lice are considered adults nine to 12 days after hatching.

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.


The most common symptom of a head-lice infestation is itching. This is caused by the louse’s saliva and feces, which cause the skin on the scalp to become irritated. The itching can be severe enough to prevent sleep, and some people scratch so much that they cause additional skin infections.

The eggs or nits of the louse appear as small white dots attached firmly to individual hairs close to the scalp.


A professional should diagnosis a head-lice infestation. Active lice infestations may be difficult to identify properly, since lice 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.

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.


Head lice are acquired by direct contact with an infested person’s hair. Sometimes lice are transferred by shared combs, brushes, hats and other hair accessories. The insects also may remain on bedding or upholstered furniture for a short time.

To prevent head-lice infestations, avoid contact with an infested person’s hair and don’t share hair-grooming tools or accessories. It is not necessary to isolate infested people or keep children with head lice home from school.


There are several treatment options. The best treatment is to use more than one method to eliminate both active lice and developing eggs, including use of an insecticide and special comb, and washing clothing and bedding in hot water and drying them in clothes dryer.

Insecticides are available over the counter and by prescription. Many contain a class of chemicals called pyrethroids as the active ingredient. Some head lice may be resistant to these products, and prescription-strength formulations may not work either. Other types of chemicals can be used when resistant head lice are identified. With any product, retreatment with an insecticide may be necessary about 10 days after the first to kill lice that hatch later, since the eggs are quite resistant to treatment.

You should 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.

To prevent reinfestation, the pillowcases, sheets, nightclothes, towels, stuffed animals, hats and other washable hair accessories of an infested person should be washed in hot water and dried in a clothes dryer on a high-heat setting. Intensive efforts to remove lice from the home by excessive vacuuming or washing are not necessary.

When To Call A Professional

You should call your physician to confirm the presence of a head-lice infestation and to obtain his or her assistance in determining whether it is active.


The prognosis of recovery from head-lice infestation is excellent. Head lice are not associated with the transmission of other types of infections, nor do they produce many symptoms other than itching. Active infestations that are treated according to directions will clear up with time.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.