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Clinical Reference Systems: Pediatric Advisor 10.0

Crab Lice

DESCRIPTION (Diagnosis must be confirmed by a physician.)

Crab lice are small, light brown, flat, pinhead insects that infest pubic hair. They attach their eggs (nits) onto pubic hair and feed on a person's tiny blood vessels.


  • Little red sores and itching in the pubic area.


Crab lice, also called pediculosis pubis, are transmitted by very close physical contact with an infested person. Although usually transmitted through sexual contact, crab lice infestation may also be caused by sleeping in a bed or sharing the towels or clothing of an infested person. The lice can remain alive in bedding for 1 to 2 weeks.

Crab lice do not leave the body voluntarily and must be treated.


With proper treatment, usually the lice are killed and the symptoms clear in about 1 week.


  1. Nix (1% permethrin) or RID (pyrethrins with piperonyl butoxide) lice-killing shampoo

    Instructions for use:

    • Apply the lice-killing shampoo to the pubic hair. Make sure all the hair is wet with the product.
    • Leave the shampoo on for the number of minutes required on the package instructions.
    • Add water until a good lather forms.
    • Rinse thoroughly and rub with a dry towel.
    • Comb the pubic hair thoroughly with a fine-tooth comb to remove any remaining nits.
    • A second treatment must be done in 7 to 10 days to kill any newly hatched lice.

  2. Contacts

    Tell your sexual partner about the crab lice because he or she may also be infested. Since these infestations are spread easily, all members of your household should also be examined carefully. Whoever else also has lice should be treated promptly to avoid spreading the lice to others.

  3. Laundry

    Dry clean or wash contaminated clothing, towels, and bed linens (sheets, pillowcases, blankets) in a washing machine with very hot water. Contaminated clothing that cannot be washed should be sealed in a plastic bag for 2 weeks to ensure death of nits.


  • Your symptoms persist after a second treatment.
  • You have other questions or concerns.

Written by David W. Kaplan, M.D., and the staff of the Adolescent Medicine Center, The Children's Hospital, Denver, Colorado.
Copyright 1999 Clinical Reference Systems