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).

Causes

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

Symptoms

Symptoms include:

• Itchiness (can range from mild to severe)

• Tiny blue-gray bumps stuck to the skin called macula caerulea

• Skin breaks and possible infection (caused by scratching)

Diagnosis

A lice infestation is diagnosed by looking closely through pubic hair for nits, nymphs, or adults. It may be difficult to find nymph or adult; here are usually few of them and they can move quickly away from light. If crawling lice are not seen, finding nits confirms that a person is infested and should be treated. If you are unsure about infestation or if treatment is not successful, see a health care provider for a diagnosis.

Treatment

Treating crabs involves applying over-the-counter shampoo or cream rinse containing permethrin or pyrethrins. Because of the potential for severe or fatal reactions, Lindane should only be used by those for whom standard treatment has failed. It should be used under the supervision of a physician. Topical malathion has also been used for resistant cases.

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 degrees Fahrenheit) 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.

• Retreat in 7-10 days.

Prevention

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.

RESOURCES:

American Academy of Dermatology
http://www.aad.org

American College of Obstetrics and Gynecology
http://www.acog.org

References:

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

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

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.

Red Book: 2003 Report of the Committee on Infectious Diseases, 26th ed.

CDC