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.

Symptoms

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.

Diagnosis

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.

Prevention

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.

Treatment