Head Lice

Head lice are parasitic insects that live in the hair and scalp of humans. They need human blood to survive.
Head lice are spread easily from person to person by direct contact.
Head lice can infest anyone, regardless of personal hygiene.
Head lice are usually treatable with lice-killing shampoos and creme rinses.
To prevent infection: 1) avoid direct contact with the head, hair, clothing, or personal belongings of a person with head lice, and 2) treat affected persons, their contacts, and their households.

What are head lice?

Head lice are parasitic insects that live in the hair and scalp of humans. The scientific name for head louse is Pediculus humanus capitis. Another name for infestation with head lice is pediculosis.

Head lice develop in three forms: nits, nymphs, and adults.

Nits: Nits are head lice eggs. They are hard to see and are often mistaken for dandruff or droplets of hairspray. Nits are found firmly attached to the hair shaft. They are oval and usually yellow to white. Nits take about 1 week to hatch.

Nymphs: Nits hatch into nymphs. Nymphs are immature adult head lice. Nymphs mature into adults about 7 days after hatching. To live, nymphs must feed on blood.

Adults: An adult louse is about the size of a sesame seed, has six legs, and is tan to greyish- white. In persons with dark hair, adult lice will look darker. Adult lice can live up to 30 days on a person's head. To live, adult lice need to feed on blood. If a louse falls off a person, it dies within 2 days.

Where are head lice found?

Head lice infestations occur worldwide.

How are head lice spread?

Head lice are spread easily from person to person by direct contact. People can get head lice by:

Coming into close contact with an already infested person. In children, contact is common during play, while riding the school bus, and during classroom activities in which children sit in groups close to each other.

Wearing infested clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons

Using infested combs, brushes, or towels

Lying on a bed, couch, pillow, carpet, or stuffed animal that has been contaminated

Lice do not jump or fly. Lice are not spread to humans from pets or other animals.

What are the signs and symptoms of head lice?

Itching -- the body's allergic reaction to the bite

Irritability

How is head lice infestation diagnosed?

Head lice infestation is diagnosed by looking closely through the hair and scalp for nits, nymphs, or adult lice.

Nits are the easiest to see. They are found "glued" to the hair shaft. Unlike dandruff or hairspray, they will not slide along a strand of hair. If you find nits more than 1/4 inch from the scalp, the infection is probably an old one.

Nymphs and adults can be hard to find; there are usually few of them, and they can move quickly from searching fingers. If lice are seen, finding nits close to the scalp confirms that a person is infested.

If you are not sure if a person has head lice, the diagnosis should be made by the local health department or a health-care provider, school nurse, or agricultural extension service worker.

Who is at risk for head lice?

Anyone can get head lice. Pre-school- and elementary-school-aged children and their families are infested most often. Girls get head lice more often than boys, and women more often than men.

What complications can result from head lice?

Scratching can lead to skin sores and skin infections.

What is the treatment for head lice infestation?

Getting rid of head lice requires treating the individual, the family, and the household.

Treat the individual and the family -- This requires using an over-the-counter or prescription lice- killing medicine. Treat only persons who are infested. Remember that all lice-killing products are pesticides. Follow these treatment steps:

Remove all clothing.
Apply lice-killing medicine, also called pediculicide [peh-DICK-you-luh-side], according to label instructions. If the affected person has extra-long hair, you may need to use a second bottle.
WARNING: Do not use a creme rinse or combination shampoo/conditioner before using lice-killing medicine. Do not re-wash hair for 1-2 days after treatment.
Have the affected person put on clean clothing after treatment.
If some live lice are still found but are moving more slowly than before treatment, do not re-treat. Comb dead and remaining live lice out of the hair. The medicine sometimes takes longer than the time recommended on the package to kill the lice.
After treatment, if no dead lice are found and lice seem as active as before, the medicine may not be working. See your health-care provider for a different medicine. Follow treatment instructions.
Remove nits and lice from the hair shaft using a nit comb, often found in lice-killing medicine packages. Flea combs used for cats and dogs can also be used.
After treatment, check, comb, and remove nits and lice from the hair every 2-3 days.
Re-treat in 7-10 days.
Check all treated persons for 2-3 weeks until you are sure all lice and nits are gone.

Treat the household:

To kill lice and nits, machine wash all washable clothing and bed linens that the infested person touched during the 2 days before they were diagnosed. Wash clothes and linens in the HOT water cycle (130 F). Dry items on the hot cycle for at least 20 minutes.
Dry clean clothing that is not washable (coats, hats, scarves, etc.). OR
Seal all non-washable items (clothing, stuffed animals, comforters, etc.) in a plastic bag for 2 weeks.
Soak combs and brushes for 1 hour in rubbing alcohol or Lysol, or wash with soap and hot water.
Vacuum the floor and furniture. Do not use lice sprays; they can be toxic if inhaled.

Cautions:

Women who are pregnant or breastfeeding should not use head-lice medications.
Consult a health-care provider before using lice-killing products on a person who has allergies, asthma, or other medical conditions.
Do not use extra amounts of lice-killing medicines.
Do not use lice-killing medicines on the eyebrows or eyelashes.

How common is head lice infection?

Head lice is a very common condition, especially among children ages 3-10. As many as 6 million to 12 million people worldwide get head lice each year. Outbreaks of head lice occur often in schools and group settings worldwide.

Is head lice an emerging infectious disease?

Yes. Head lice is an increasing problem because lice-killing medicines are becoming less effective.

How can head lice be prevented?

Educate parents and schools about head lice. All parents should know that outbreaks of head lice have nothing to do with a family's income, social status, or level of personal hygiene.
Avoid direct contact with a person who has lice, or with their clothing or personal belongings.
Watch for signs of lice, such as frequent head scratching. Nits do not cause symptoms, but they can be seen on the hair shaft; they are yellow-white and oval-shaped.
Teach children not to share combs, brushes, scarves, hair ribbons, helmets, headphones, hats, towels, bedding, clothing, or other personal items.
Examine household members and close contacts of a person with head lice, and treat if infested.
Make sure schools, camps, and child-care centers provide separate storage areas (cubbies or lockers) and widely spaced coat hooks for clothing and other personal articles. They should assign sleeping mats and bedding to only one child and store these separately. They should wash dress-up clothes and play costumes between use by different children. During an outbreak, costumes should not be used in the classroom.
Exclude children with head lice from school or day care according to the institution's policy.

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health-care provider. If you have questions about the disease described above, consult a health-care provider.