Pubic lice are not an infection but an infestation by small, wingless insects. Their scientiﬁc name is Phthirus pubis, but they are commonly called crabs, because of their crablike claws, which they use to grasp hair. Usually this is pubic hair,
but crabs have been found in armpit hair and beards and may even attach to eye- lashes. The lice may also settle around the anus and in the hair on the legs and trunk. The typical infestation involves fewer than a dozen lice.
An adult louse has a small, ﬂat body up to 2 millimeters across. It is either grayish white or brown, colors that blend in with the surroundings and make the insect difﬁcult to see. The lice lay shiny white eggs, called nits, at the bottom of the hair shafts, where they hatch 7 to 10 days later.
Sometimes pubic lice cause no symptoms. Most often, however, they cause small red sores and itching, which becomes worse at night. If lice infest eye- brows or eyelashes, they can cause the eyes to become inﬂamed.
While unaffected by ordinary soaps, pubic lice can be destroyed with a special shampoo or lotion containing malathion or carbaryl. Typically, the medication works in a single treatment, but it is important to follow the directions very care- fully; if used incorrectly, the chemicals can be toxic. Itching may persist for a few days after successful treatment. Contact your physician, however, if you develop redness, swelling, tenderness, or drainage around the areas of infestation or if the lotion comes into contact with your eyes.
If you have pubic lice, it is not enough to kill only those that are attached to your body. You must also wash your clothes and bedding in water hotter than 140 degrees Fahrenheit, since the lice can survive without a human host for 1 to 2 days.
Since pubic lice are nearly always spread by close physical contact, the affected person’s sexual partners also should be treated. They should avoid inti- mate contact with others until the lice are entirely gone.