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Head Lice

What are the symptoms of a head lice infestation?

The earliest and most common symptom of a head lice infestation is itching, particularly in the area behind the ears and at the nape of the neck. Intense scratching may lead to secondary bacterial infection.

How are head lice spread?

Head lice can be passed from person to person through direct contact. But they also can be transferred indirectly among clothing items when coats, hats and scarves hang or are stored touching one another (in cloak rooms or when these items are placed against one another on coat hooks or racks). Head lice also can be spread when infested hair brushes or combs are shared or when infested bedding, towels or shower caps are shared. Once present in a home, school or institutional environment, head lice usually spread rapidly.

There are many misconceptions about head lice. They do not transmit communicable diseases. They do not jump or fly; they can only crawl. Head lice depend completely on their host for nourishment; their only source of food is human blood. The prevalence of head lice infestation is no different in individuals with long hair than in those with short hair. Head lice seldom occur on eyebrows or eyelashes. They infest persons from all socioeconomic levels, without regard for age, race, sex or standards of personal hygiene. Animals are not a source of human lice.

How long do head lice live?

The life span of an adult louse on a host ranges up to 30 days. During this time, the female head louse can deposit about 90 eggs. After incubating for seven to 10 days, the nits hatch and, after another 10 days, mature into adult head lice and the cycle begins again. Off the host, adult head lice can live about two to four days at 74 degrees Fahrenheit (F) and one to two days at 86 degrees. Nits will remain alive off the host for up to 10 days; they will not hatch at or below room temperature (68 degrees F).

How are head lice infestations treated?

Both prescription and over-the-counter remedies are effective in treating head lice. But it is important that pregnant women and infants be treated under the direction of a physician because of concerns about potentially adverse effects. Be careful not to use topical preparations more frequently and over longer periods of time than directed. Overuse of these preparations may cause dermatitis or result in absorption of potentially toxic quantities of the drug. Since agents that kill lice may not kill nits completely even when used according to directions the U. S. Centers for Disease Control and Prevention (CDC) recommends that infested patients be treated twice. The interval between treatments should approximate the incubation period for nits (seven to 10 days) so the second application will kill any newly hatched parasites. Waiting longer than 10 days to apply a second treatment may allow some parasites to mature and lay more eggs.
All persons who have head lice in a household should be treated. To treat an infested person--

  • Remove all clothing;
  • Apply head lice medication according to label instructions (do not bathe before treatment), using a towel to protect the eyes;
  • Have the person bathe and put on clean clothing after treatment; and
  • Repeat treatment in seven to 10 days.

Special fine-tooth combs (nit combs) are readily available and can be used to scrape nits and lice off the hair shaft. Combing out nits and lice after proper treatment is not necessary to eliminate infestation, but it may be used for cosmetic reasons or may be required by school "nit-free" policies or by health authorities. Parents and guardians should check treated children for lice and nits daily for two or three weeks after treatment.

Should objects (e.g., clothing, furniture, etc.) be treated?

Objects that are able to harbor head lice and serve as vehicles of transmission should be treated.

  • Exposing lice and nits to temperatures above 125 degrees F for 10 minutes is lethal. Most personal articles of clothing and bedding can be disinfested by machine washing in hot water or machine drying for at least 20 minutes using the hot cycle. Be sure to allow time between loads for water to reheat to the disinfesting temperature.
  • Place non-washable personal articles of clothing or bedding in the dryer on high heat for at least 20 minutes, dry clean or seal non-washable fabrics in a plastic bag for a minimum of 10 days.
  • Place combs and brushes in a pan of water and heat on a stove to about 150 degrees F for 10 minutes. If heating may damage combs or brushes, soak them for one hour in a phenol solution (e.g., Lysol®). To prevent the spread of head lice, do not share combs, brushes, hats, coats, towels or other articles that come in contact with the head, neck and shoulders.
  • Thoroughly vacuum or clean car seats, bus seats, and individual infant and car seats according to manufacturer's directions.
  • Fumigating rooms and using insecticidal sprays on furniture and carpets are not recommended to kill head lice; thorough vacuuming of houses and rooms inhabited by infested persons is sufficient.

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