In this scalp infested with head lice, there are 2 scabs from scratching and a few white nits on the hair shaft (which look like flakes of dandruff but are actually glued to the hair). Numerous tiny, white lice eggs (nits) glued to the hair shaft are seen in this person with head lice. Nits are the egg cases of lice. They are seen here firmly attached to the hair. This is a microscopic picture of the head louse.
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Head Lice (Pediculosis Capitis)  Information for adults

Picture of Head Lice (Pediculosis Capitis): In this scalp infested with head lice, there are 2 scabs from scratching and a few white nits on the hair shaft (which look like flakes of dandruff but are actually glued to the hair). Divider line
In this scalp infested with head lice, there are 2 scabs from scratching and a few white nits on the hair shaft (which look like flakes of dandruff but are actually glued to the hair).
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Overview
Head lice (pediculosis capitis) are highly contagious, and the most prominent symptom of a head lice infestation includes intense scalp itching.

The human head louse is a tiny insect that feeds on human blood. The female louse lays eggs (nits) on the hair shaft close to the scalp, and they become glued to the hair shaft. The nits hatch about 8–10 days later and begin to feed with any remaining adults. The nits can stay alive for a long period of time off of the body, such as on hairbrushes, furniture, or linens.
Who's At Risk
Head lice occur in people of all ages and races. Males are affected somewhat less than females. Children are most likely to become affected by a head lice infestation, and epidemics can occur in schools, day cares, and nurseries, but adults may become infected, most often through contact with infected children. Nursing home epidemics have also occurred. In the United States, blacks are less commonly affected because the shape of the louse claw is better suited to grabbing onto the hairs of those who are white or Asian.
Signs and Symptoms
The most common locations for head lice infestations include:
  • Scalp, especially the hairline near the neck
  • Behind the ears
  • Neck
Moving lice or non-moving nits may be seen on the scalp and hair. Each louse is approximately 1–2 mm long and is white-gray in color. The white nits are smaller (0.5 mm), are firmly attached to the hair shaft, and are usually located very close to the scalp. In longer-standing infestations, the nits may be farther away from the scalp. In addition, small, red bumps may be seen on the scalp, neck, and shoulders. If scratched aggressively, these bumps may become scabbed.
Self-Care Guidelines
The following self-care measures may be helpful if you think you have head lice:
  • Search for lice and nits on wet hair using a fine-toothed comb (louse comb). Examine the scalp in strong light, using a magnifying glass if necessary.
  • Use an over-the-counter medication for head lice exactly as directed. These medicines are insecticides and should not be applied in greater quantity or more frequently than recommended. These medications are not recommended for children younger than 2 years old.
  • Wash household items such as bed linens, towels, and hats in hot water, and dry them using the hot cycle for at least 20 minutes.
  • Wash any object that the infected person has come into contact with in the past 48 hours in hot water for at least 5 minutes.
  • Seal potentially contaminated but non-washable objects in plastic bags for 2 weeks. (The lice will die within 2 days, and the nits will hatch and die within 2 weeks.)
  • Vacuum any floors and furniture that have been in contact with the infected person.
  • Do not share combs, hair brushes, hats, towels, bedding, clothing, headphones, stuffed toys, or other personal items with someone who has head lice.
When to Seek Medical Care
See your doctor if self-care measures have not successfully killed off (eradicated) the lice infestation. Also call the doctor if you see any signs of bacterial infection on or near the head, such as redness, swelling, pain, or pus. Additionally, call the doctor before using any louse medicines if you are pregnant.
Treatments Your Physician May Prescribe
In order to make a diagnosis of head lice, the doctor must see a louse or a nit on the scalp. Occasionally, a Wood's lamp is used to look for lice and nits. In this procedure, the doctor shines a black light at the scalp, and the insects and eggs appear as yellow-green fluorescent spots under this light.

Once the diagnosis of head lice has been confirmed, the doctor may recommend one or more of the following treatments in addition to the self-care measures outlined above:
  • Permethrin lotion or shampoo
  • Malathion lotion
  • Lindane lotion, cream, or shampoo (not used as much anymore due to potential toxicity)
  • Ivermectin pills

References

Bolognia, Jean L., ed. Dermatology, pp.1324-1326. New York: Mosby, 2003.
Last Updated: 22 Dec 2008