McKesson Clinical Reference Systems: Women's Health Advisor 2002.2

What are crab lice?

Crab lice are tiny wingless insects that look like crabs when seen under a microscope. They are 1 to 3 millimeters long, or less than 1/8 inch. They live in hairy areas of the human body.

Lice bite through the skin to suck blood. They also lay eggs and attach them to hairs. These eggs, called nits, hatch in 8 to 10 days, producing more lice.

How do people get crab lice?

Crab lice are passed from person to person through close body contact. The lice can live up to 1 week away from the body, so you can get the lice from such items as bed sheets, towels, and sleeping bags.

What are the symptoms?

The most common symptom is itching. At first, however, when you have only a few lice, you may have no symptoms.

You may see one or more lice or nits in your pubic hair. The nits look like tiny white dots attached firmly to a hair. They look like dandruff. Dandruff, however, is easily brushed out of the hair. Nits cannot be brushed or flicked off. They must be pulled off the hair with your fingers.

Besides the pubic hair, crab lice sometimes live in other hairy areas, such as the chest, abdomen, underarms, and head. They may even be in facial hair, such as beards, eyebrows, and eyelashes.

How is it diagnosed?

Your health care provider looks for lice or nits in your pubic hairs or on other parts of your body.

How is it treated?

Nonprescription products, such as Nix or Rid shampoo, can be used to kill lice and nits. If a nonprescription product does not kill the lice, your health care provider may prescribe a shampoo containing the medicine lindane.

Lather the shampoo into the area where the lice are. Leave the shampoo on for several minutes, then thoroughly rinse it out. One treatment is usually enough, but your health care provider may recommend that you repeat the shampooing in 1 week.

If you are pregnant, check with your health care provider before you use any type of anti-lice shampoo. Pregnant women and women who are breast-feeding should not use lindane. Do not use prescription lice medicines on children without checking first with your provider. Medicines other than lindane are safer for preschool children. Lindane can cause seizures if it is not used correctly. If you use a lindane shampoo, carefully follow the directions for its use, and do not overuse it.

After treatment the dead nits will still be on the hairs. You must remove all of them. Otherwise, if you see nits several days after your treatment, you will not know if they are old dead nits or a new infestation. Use a fine-tooth comb, tweezers, or your fingers to remove the dead nits.

If the lice are in your eyebrows or eyelashes, you will probably need to carefully remove them by hand. In some cases, medicine that is safe for the eyes can be used.

You also need to remove lice from your clothing, towels, and bedding. All these items must be thoroughly washed or dry cleaned.

What can be done to help prevent crab lice?

The best way to prevent crab lice is to have one sexual partner or avoid sexual contact. Condoms are not good protection against crab lice because they do not cover the hairy areas where the lice live. You should also avoid contact with contaminated clothing, bed clothing, and toilet seats.

This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.