About Head Lice

Overview

Head lice, or Pediculus humanus capitis, are parasitic insects that feed on human blood. You can find them mostly on your head, but also on your eyebrows and eyelashes. Adult head lice are roughly 2 – 3 mm long (about the size of a sesame seed).

Both over-the-counter and prescription medications are available to treat head lice in your hair (infestation).

Symptoms

People with head lice may not have symptoms, particularly with a first infestation or when an infestation is light. Itching (pruritus) is the most common symptom of head lice infestation. It is caused by an allergic reaction to louse bites. It may take four to six weeks for itching to appear the first time a person has head lice.

Other symptoms may include the following:

• A tickling feeling or a sensation of something moving in the hair
• Irritability and sleeplessness
• Sores on the head caused by scratching, which can sometimes become infected with bacteria normally found on your skin

Head lice do not transmit any disease and therefore are not considered a health hazard.

Who is at risk?

In the United States, infestation with head lice is most common among preschool- and elementary school-age children and their household members and caretakers.

There is not reliable data on how many people get head lice each year in the United States; however, an estimated 6 – 12 million infestations occur each year in the United States among children 3 – 11 years of age. Some studies suggest that girls get head lice more often than boys, probably due to more frequent head-to-head contact.

In the United States, infestation with head lice is much less common among African American persons than among persons of other races. The head louse found most frequently in the United States may have claws that are better adapted for grasping the shape and width of some types of hair, but not others.

How it spreads

Head lice mainly spread by direct contact with the hair of a person infested with lice. Head lice move by crawling; they cannot hop or fly. Adult lice can live on a person's head for about 30 days. However, they will die within two days if they fall off a person and cannot feed. Adult female head lice are usually larger than males and can lay about six eggs each day. Nits (lice eggs) cannot hatch and usually die within a week if they are not kept at the same temperature as those found close to the scalp. Nits take about a week (range 6 – 9 days) to hatch into nymphs (young lice). Nymphs look similar to adult lice but are very small (size of a pinhead); they take about seven days to mature into adult lice.

The most common way to get head lice is by head-to-head contact with a person who already has head lice. This contact can be common among children playing at places like school or the home. Getting head lice is not related to cleanliness of you or your environment.

Although not as common, head lice may spread by:

• Wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons worn by an infested person
• Using infested combs, brushes, or towels
• Lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person

Contracting lice from a wig or hairpiece is extremely unlikely. Especially if the wig or hairpiece hasn't been worn in the past 48 hours by a person with head lice.

Head lice can survive under water for several hours but are unlikely to spread in a swimming pool. Chlorine levels in pool water do not kill head lice.

Animals do not get or spread head lice.

Prevention

Take these steps to help prevent and control the spread of head lice:

• Avoid head-to-head (hair-to-hair) contact during play and other activities at home, school, and elsewhere (sports activities, playground, slumber parties, camp).
• Do not share clothing such as hats, scarves, coats, sports uniforms, hair ribbons, or barrettes.
• Do not share combs, brushes, or towels. Disinfest combs and brushes used by an infested person by soaking them in hot water (at least 130°F) for 5 – 10 minutes.
• Do not lie on beds, couches, pillows, carpets, or stuffed animals that have recently been in contact with a person infested with head lice.
• Machine wash and dry clothing, towels, bed linens, and other items that a person infested with lice wore or used during the two days before treatment. Use the hot water (130°F) laundry cycle and the high heat drying cycle. If you can't wash or dry clean items, seal them in a plastic bag and store them for two weeks.
• Vacuum the floor and furniture, particularly where the infested person sat or lay. However, spending much time and money on housecleaning activities is not necessary to avoid reinfestation by lice or nits that may have fallen off the head or crawled onto furniture or clothing.
• Do not use fumigant sprays or fogs; they are not necessary to control head lice and can be toxic if inhaled or absorbed through the skin.

To help control a head lice outbreak in a community, school, or camp, teach children to avoid activities that may spread head lice. For example, teach children to

• Avoid hair-to-hair contact during play.
• Not to share clothing such as hats, hair ribbons, barrettes, scarves, coats, or sports uniforms.
• Not to share combs, brushes, or towels.

Diagnosis

Misdiagnosis of head lice infestation is common. Finding a live nymph (baby louse) or adult louse on the scalp or hair is the best way to diagnose a head lice infestation.

Because adult and nymph lice are very small, move quickly, and avoid light, they may be difficult to find. A fine-toothed louse comb may help you find lice.

If you do not see crawling lice, look for nits attached firmly within ¼ inch of the base of hair shafts. You will often see nits on hair behind the ears and near the back of the neck. Nits that are attached more than ¼ inch from the base of the hair shaft are almost always hatched or dead.

Although head lice and nits can be visible with the naked eye, a magnifying lens may help to find crawling lice or nits. Nits are often confused with other particles found in hair such as dandruff, hair spray droplets, and dirt particles.

If you do not see nymphs or adults, and the only nits found are more than ¼ inch from the scalp, then the infestation is probably old and does not need treatment.