Crab Lice
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Crab Lice

(Pubic Lice; )

En Español (Spanish Version)


Crabs, or pubic lice, are tiny, barely visible parasites (scientific name Pthirus pubis ) that live in the pubic area and cause itching. ("Lice" is plural; the singular is "louse"). Pubic lice are commonly called crabs because they are shorter and rounder than head and body lice, making them resemble crabs. They are usually found in the pubic hair, but can also be found in other body areas with short hair (eg, eyelashes, eyebrows, armpits, mustache).

Pubic Louse

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Crabs are parasites that can infect the human body. They are spread by personal contact, usually during sexual activity. They may also spread by sharing personal items, such as bedding, towels, and clothing, but this form of transmission is less common.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors include:

  • Sexual contact with people who have crabs
  • Contact with contaminated items, such as:
    • Bedding
    • Towels
    • Clothing
    • Toilet seats
    • Furniture


Symptoms include:

  • Itchiness (can range from mild to severe)
  • Tiny blue-gray bumps stuck to the skin called macula caerulea
  • Skin breaks and possible bacterial infection (caused by scratching)


The doctor will ask about your symptoms and medical history, and perform a physical exam. He or she will examine your pubic area for lice, lice eggs (called nits), and macula caerulea .


Treating crabs involves applying over-the-counter shampoo or cream rinse containing permethrin or pyrethrins. For resistant cases, topical malathion (a highly effective prescription medication approved only for patients older than 6 years) or lindane may be used.

Lindane, a second line treatment, should only be prescribed to patients who are unable to take other medications or who have not responded to them. According to the Food and Drug Administration’s warning, lindane can rarely cause serious side effects, including seizure and death. Those especially susceptible are infants, the elderly, children and adults weighing under 110 lbs, and individuals with other skin conditions. Lindane is a toxin and should not be overused. Patients are given small amounts (1-2 oz) of the shampoo or lotion and instructed to apply a very thin layer and not to reapply. For more information, visit the Center for Drug Evaluation and Research website .

Treatment steps:

  • Wash the infested area, and then towel dry.
  • Thoroughly saturate hair with lice medication. If using permethrin or pyrethrins, leave medication on for 10 minutes. (If using lindane, leave on for only four minutes.)
  • Thoroughly rinse off medication with water. Dry off with a clean towel.
  • Following treatment, most lice eggs will still be attached to hair shafts. You can remove them with your fingernails or tweezers.
  • Put on clean underwear and clothing after treatment.
  • If you have lice in your eyebrows, you may be directed to coat your eyebrows thoroughly with petroleum jelly.
  • To kill any lice and nits that may be left on clothing or bedding, wash those items used during the 2-3 days before treatment. Use the hot water cycle (130°F) of the washing machine. Use the hot cycle of the dryer for at least 20 minutes to dry clothes.
  • Dry clean clothing that is not washable.
  • Avoid any sexual partners until they have been treated.
  • If necessary, retreat in 7 to 10 days.


To reduce the chance of getting crabs or spreading crabs:

  • Limit sexual partners.
  • Watch for signs of crabs, such as itching in the genital area.
  • If you or someone in your house has had crabs, thoroughly wash and dry bedding, towels, clothing, and vacuum carpeting and upholstered furniture.
  • If you have had crabs, inform any sexual partners that they are at risk for crabs, and avoid sexual activity until partners have been treated.


American Academy of Dermatology

American College of Obstetrics and Gynecology


Communicable Disease Control (CDC) Network
Province of Manitoba

Health Canada


American Academy of Dermatology website. Available at: http://www.aad.org .

American Academy of Pediatrics. Red Book: 2006 Report of the Committee on Infectious Diseases. 27th ed. 2006.

Federal Drug Administration website. Available at http://www.fda.gov .

Kleigman RM, Jensen HB, Behrman RE, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, PA: Saunders Elsevier; 2007.

Lindane shampoo and lindane lotion. Center for Drug Evaluation and Research. US Food and Drug Administration website. Available at: http://www.fda.gov/cder/drug/infopage/lindane/default.htm . Accessed March 12, 2007.

Medication guide lindane (LIHN-dane) lotion USP, 1%. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/drug/infopage/lindane/lindaneLotionGuide.htm . Accessed March 12, 2007.

Medication guide lindane (LIHN-dane) shampoo USP, 1%. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/drug/infopage/lindane/lindaneShampooGuide.htm . Accessed March 12, 2007.

The National Center for HIV, STD, and TB Prevention. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/nchstp/od/nchstp.html .

Revised lindane lotion label. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/foi/label/2003/006309lotionlbl.pdf . Accessed March 12, 2007.

Revised lindane shampoo label. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/foi/label/2003/006309shampoolbl.pdf . Accessed March 12, 2007.

Last reviewed November 2007 by Kari L. Kassir, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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