Crab Lice

What are crab lice?

Crab lice are tiny wingless insects that look like crabs when viewed with a microscope. They are 1 to 3 millimeters long, or less than 1/8 inch. They live in hairy areas of the human body (usually the pubic hair).

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 for 1 to 2 weeks 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 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.

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?

Lice will not go away without proper treatment. Nonprescription anti-lice products, such as Nix rinse or RID shampoo, can be used to kill lice and nits.

Use the anti-lice rinse or shampoo according to the instructions on the package or your provider's directions. One treatment is usually enough, but your provider may recommend that you repeat the treatment in 1 week.

If a nonprescription product does not kill the lice, your provider may prescribe a shampoo containing the medicine lindane. However, the nonprescription medicines are safer than lindane for preschool children. Lindane can cause seizures if it is not used correctly. Carefully follow the directions for its use, and do not overuse it. If you are pregnant, check with your health care provider before you use any type of anti-lice product.

Do not have sex until you have completed the treatment and the lice and nits are all gone. You need to remove lice from your clothing, towels, and bedding. Machine wash all items that you used in the last 3 days before you started treatment. Use the hot water cycle to wash the items. Use the hot setting on your dryer for at least 20 minutes to dry the laundry. Anything that can't be washed this way needs to be dry cleaned. Contaminated clothing that cannot be washed or dry cleaned should be sealed in a plastic bag for 2 weeks to ensure death of nits.

What can be done to help prevent crab lice?

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

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.