Patient information: Pubic lice (Phthirus pubis)

PUBIC LICE OVERVIEW

There are three types of lice that infest humans: the head louse (Pediculosis humanus capitis), the body louse (Pediculosis humanus corporis), and the pubic louse or "crab" (Phthirus pubis). Pubic lice (crabs) are most often spread from one person to another through sexual contact, and they can be found in all parts of the world. Men and women of all races can be affected.

This topic reviews the diagnosis and treatment of public lice. Head lice are discussed separately. (See "Patient information: Head lice (Pediculosis capitis)".)

PUBIC LICE DESCRIPTION

The pubic or crab louse is small (2 to 3 millimeters, or 0.08 to 0.12 inches) and round. It can be difficult to see unless it is filled with blood from a recent feeding. Four of its six legs have crab-like claws which allow it to grasp tightly onto hairs (picture 1). Female lice live for three to four weeks, during which time she lays up to three eggs per day. The eggs hatch after about eight days.

Although these lice primarily affect the pubic area, they may also be found on other areas of the body (eyebrows, armpits, beard, mustache). Pubic lice are not found on the head. (See "Patient information: Head lice (Pediculosis capitis)".)

Animals do not carry or spread pubic lice. However, pubic lice can move and may be spread from one person to another on clothing, bedsheets, towels, or other shared items.

PUBIC LICE SYMPTOMS

Most people infested with pubic lice complain of itching in the pubic or genital area. Other parts of the body, such as the armpits, may also be itchy if lice are present. Pale bluish spots may be seen on the skin a result of repeat feedings in the same area.

Children of parents infested with pubic lice occasionally develop an infestation of the eyelashes or eyebrows. This can cause an itching or burning sensation in the eyes, and the eyelids may appear red and irritated.

PUBIC LICE DIAGNOSIS

Pubic lice are diagnosed by examining the genital area for lice or their eggs (picture 2). Because pubic lice are a sexually transmitted infection (STI), testing for other STIs, such as gonorrhea, chlamydia, and HIV, is often recommended. (See "Patient information: Gonorrhea" and "Patient information: Chlamydia" and "Patient information: Testing for HIV".)

PUBIC LICE TREATMENT

The recommended treatment for pubic lice is an insecticide lotion or cream that is applied to the skin. The most commonly used insecticides include:

• Permethrin (Nix®, Rid®)
• Pyrethrin (A-200®, Pronto®, Tisit®)

Alternately, the person may take a pill (ivermectin/Stromectol®), which is taken once and then repeated two weeks later. We do not suggest shaving the pubic hair.

The skin should be cool and dry to minimize absorption of the insecticide through the skin. The lotion/cream is usually applied to the skin and hair in the pubic area, but not inside the vagina or rectum. The lotion should be left on for 10 minutes and then rinsed off.

Visible lice eggs (nits) can be removed using fingernails, a fine-tooth comb, or tweezers. If symptoms are still present a week after treatment, the person should be examined again and retreated if necessary.

Children with an infestation of the eyelashes may be treated by applying petroleum jelly (Vaseline®) to the eyelids to dislodge the lice and eggs. In more severe cases, a healthcare provider may recommend a prescription treatment.

Anyone who is diagnosed with pubic lice should notify their sexual partners from the previous month of the need to be examined and tested for other sexually transmitted infections. Clothing, towels, and bedding used within 72 hours before treatment should be washed and dried in an electric dryer on the hot setting or dry cleaned.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Head lice (Pediculosis capitis)
Patient information: Gonorrhea
Patient information: Chlamydia
Patient information: Testing for HIV

Professional Level Information:
Approach to the patient with a scalp eruption
Pediculosis

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies, and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/ency/article/000841.htm, available in Spanish)

• Center for Disease Control and Prevention

      (www.cdc.gov/lice/)

• The Nemours Foundation

      (http://kidshealth.org/parent/infections/parasitic/pubic_lice.html)

UpToDate wishes to acknowledge Kelly Crowley for her contributions to this topic.

[1-3]