Adult pubic lice are 1.1–1.8 mm in length. Pubic lice typically are found attached to hair in the pubic area but sometimes are found on coarse hair elsewhere on the body (for example, eyebrows, eyelashes, beard, mustache, chest, armpits, etc.).

Pubic lice infestations (pthiriasis) are usually spread through sexual contact. Dogs, cats, and other pets do not play a role in the transmission of human pubic lice.

Both over-the-counter and prescription medications are available for treatment of pubic lice infestations.

Causal Agent:

Pthirus pubis, the pubic or crab louse, is an insect of the order Psocodea and is an ectoparasite whose only host are humans.

Life Cycle:

Pubic lice (Pthirus pubis) have three stages: egg, nymph and adult. Eggs (nits) are laid on a hair shaft (1). Females will lay approximately 30 eggs during their 3–4 week life span. Eggs hatch after about a week and become nymphs, which look like smaller versions of the adults. The nymphs undergo three molts (2,3,4) before becoming adults (5) . Adults are 1.5–2.0 mm long and flattened. They are much broader in comparison to head and body lice. Adults are found only on the human host and require human blood to survive. If adults are forced off the host, they will die within 24–48 hours without a blood feeding. Pubic lice are transmitted from person to person most-commonly via sexual contact, although fomites (bedding, clothing) may play a minor role in their transmission.

What are pubic lice?

Pubic lice (also called crabs) are tiny insects which usually live in the pubic or genital area of humans. They are also sometimes found on other coarse body hair, such as hair on the legs, armpits, mustache, beard, eyebrows, or eyelashes. Pubic lice on the eyebrows or eyelashes of children or teens may be a sign of sexual exposure or abuse.

Pubic lice are parasites, and they need to feed on human blood to survive. They are one of the three types of lice that live on humans. The other two types are head lice and body lice. Each type of lice is different, and getting one type does not mean that you will get another type.

How do pubic lice spread?

Pubic lice move by crawling, because they cannot hop or fly. They usually spread through sexual contact. Occasionally, they may spread through physical contact with a person who has pubic lice, or through contact with clothing, beds, bed linens, or towels that were used by a person with pubic lice. You cannot get pubic lice from animals.

Who is at risk for pubic lice?

Since they spread mainly through sexual contact, pubic lice are most common in adults.

What are the symptoms of pubic lice?

The most common symptom of pubic lice is intense itching in the genital area. You may also see nits (lice eggs) or crawling lice.

How do you know if you have pubic lice?

A diagnosis of a pubic lice usually comes from seeing a louse or nit. But lice and nits can be difficult to find because there may be only a few present. Also, they often attach themselves to more than one hair, and they do not crawl as quickly as head and body lice. Sometimes it takes a magnifying lens to see the lice or nits.

People who have pubic lice should also be checked for other sexually transmitted diseases, and their sexual partners should also be checked for pubic lice.

What are the treatments for pubic lice?

The main treatment for pubic lice is a lice-killing lotion. Options include a lotion that contains permethrin or a mousse containing pyrethrins and piperonyl butoxide. These products are available over-the-counter without a prescription. They are safe and effective when you use them according to the instructions. Usually one treatment will get rid of the lice. If not, you may need another treatment after 9-10 days.

There are other lice-killing medicines that are available with a prescription from your health care provider.

You should also wash your clothes, bedding, and towels with hot water, and dry them using the hot cycle of the dryer.

Pubic (“crab”) lice infestation is found worldwide and occurs in all races and ethnic groups and in all levels of society. Pubic lice usually are spread through sexual contact and are most common in adults. Occasionally pubic lice may be spread by close personal contact or contact with articles such as clothing, bed linens, and towels that have been used by an infested person. Pubic lice found on the head or eyelashes of children may be an indication of sexual exposure or abuse.

Pubic lice do not transmit disease; however, secondary bacterial infection can occur from scratching of the skin.

Pubic (“crab”) lice are not known to transmit any disease. Itching (“pruritus”) in the pubic and groin area is the most common symptom of pubic lice infestation. As with other lice infestations, intense itching leads to scratching which can cause sores and secondary bacterial infection of the skin.

Visible lice eggs (“nits”) or lice crawling or attached to pubic hair, or less commonly other hairy areas of the body (eyelashes, eyebrows, beard, mustache, armpits, chest, back) are other signs of pubic lice infestation.

Pubic lice on the head (eyelashes or eyebrows) of a child may be an indication of sexual exposure or abuse.

Persons infested with pubic lice should be evaluated for other sexually transmitted diseases (STDs).

Pubic lice are short and crab-like and appear very different from head and body lice. Pubic lice infestation is diagnosed by finding a “crab” louse or eggs on hair in the pubic region or, less commonly, elsewhere on the body (eyebrows, eyelashes, beard, mustache, armpit, perianal area, groin, trunk, scalp). Although pubic lice and nits can be large enough to be seen with the naked eye, a magnifying lens may be necessary to find lice or eggs.

A lice-killing lotion containing 1% permethrin or a mousse containing pyrethrins and piperonyl butoxide can be used to treat pubic (“crab”) lice. These products are available over-the-counter without a prescription at a local drug store or pharmacy. These medications are safe and effective when used exactly according to the instructions in the package or on the label.

Lindane shampoo is a prescription medication that can kill lice and lice eggs. However, lindane is not recommended as a first-line therapy. Lindane can be toxic to the brain and other parts of the nervous system; its use should be restricted to patients who have failed treatment with or cannot tolerate other medications that pose less risk. Lindane should not be used to treat premature infants, persons with a seizure disorder, women who are pregnant or breast-feeding, persons who have very irritated skin or sores where the lindane will be applied, infants, children, the elderly, and persons who weigh less than 110 pounds.

Malathion* lotion 0.5% (Ovide*) is a prescription medication that can kill lice and some lice eggs; however, malathion lotion (Ovide*) currently has not been approved by the U.S. Food and Drug Administration (FDA) for treatment of pubic (“crab”) lice.

Both topical and oral ivermectin have been used successfully to treat lice; however, only topical ivermectin lotion currently is approved by the U.S. Food and Drug Administration (FDA) for treatment of lice. Oral ivermectin is not FDA-approved for treatment of lice.

How to treat pubic lice infestations: (Warning: See special instructions for treatment of lice and nits on eyebrows or eyelashes. The lice medications described in this section should not be used near the eyes.)

1. Wash the infested area; towel dry.
2. Carefully follow the instructions in the package or on the label. Thoroughly saturate the pubic hair and other infested areas with lice medication. Leave medication on hair for the time recommended in the instructions. After waiting the recommended time, remove the medication by following carefully the instructions on the label or in the box.
3. Following treatment, most nits will still be attached to hair shafts. Nits may be removed with fingernails or by using a fine-toothed comb.
4. Put on clean underwear and clothing after treatment.
5. To kill any lice or nits remaining on clothing, towels, or bedding, machine-wash and machine-dry those items that the infested person used during the 2–3 days before treatment. Use hot water (at least 130°F) and the hot dryer cycle.
6. Items that cannot be laundered can be dry-cleaned or stored in a sealed plastic bag for 2 weeks.
7. All sex partners from within the previous month should be informed that they are at risk for infestation and should be treated.
8. Persons should avoid sexual contact with their sex partner(s) until both they and their partners have been successfully treated and reevaluated to rule out persistent infestation.
9. Repeat treatment in 9–10 days if live lice are still found.
10. Persons with pubic lice should be evaluated for other sexually transmitted diseases (STDs).

Special instructions for treatment of lice and nits found on eyebrows or eyelashes:

• If only a few live lice and nits are present, it may be possible to remove these with fingernails or a nit comb.
• If additional treatment is needed for lice or nits on the eyelashes, careful application of ophthalmic-grade petrolatum ointment (only available by prescription) to the eyelid margins 2–4 times a day for 10 days is effective. Regular petrolatum (e.g., Vaseline)* should not be used because it can irritate the eyes if applied.

*Use of trade names is for identification purposes only and does not imply endorsement

This information is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the parasites described above or think that you may have a parasitic infection, consult a health care provider.

Persons who have pediculosis pubis (i.e., pubic lice) usually seek medical attention because of pruritus or because they notice lice or nits on their pubic hair. Pediculosis pubis is caused by the parasite Phthirus pubis and is usually transmitted by sexual contact.

Diagnosis

The clinical diagnosis is based on typical symptoms of itching in the pubic region. Lice and nits can be observed on pubic hair.

Treatment

Recommended Regimens for Pediculosis Pubis

Permethrin 1% cream rinse applied to affected areas and washed off after 10 minutes

OR

Pyrethrin with piperonyl butoxide applied to the affected area and washed off after 10 minutes

Alternative Regimens

Malathion 0.5% lotion applied to affected areas and washed off after 8–12 hours

OR

Ivermectin 250 µg/kg body weight orally, repeated in 7–14 days

Reported resistance to pediculicides (permethrin and pyrethrin) has been increasing and is widespread. Malathion can be used when treatment failure is believed to have occurred as a result of resistance. The odor and longer duration of application associated with malathion therapy make it a less attractive alternative compared with the recommended pediculicides. Ivermectin has limited ovicidal activity. Ivermectin might not prevent recurrences from eggs at the time of treatment, and therefore treatment should be repeated in 7–14 days. Ivermectin should be taken with food because bioavailability is increased, thus increasing penetration of the drug into the epidermis. Adjustment of ivermectin dosage is not required for persons with renal impairment; however, the safety of multiple doses among persons with severe liver disease is unknown. Lindane is not recommended for treatment of pediculosis because of toxicity, contraindications for certain populations (pregnant and breastfeeding women, children aged <10 years, and those with extensive dermatitis), and complexity of administration.

Other Management Considerations

The recommended regimens should not be applied to the eyes. Pediculosis of the eyelashes should be treated by applying occlusive ophthalmic ointment or petroleum jelly to the eyelid margins 2 times/day for 10 days. Bedding and clothing should be decontaminated (i.e., machine washed and dried by using the heat cycle or dry cleaned) or removed from body contact for at least 72 hours. Fumigation of living areas is unnecessary. Pubic hair removal has been associated with atypical patterns of pubic lice infestation and decreasing incidence of infection. Persons with pediculosis pubis should be evaluated for HIV, syphilis, chlamydia, and gonorrhea.

Follow-Up

Evaluation should be performed after 1 week if symptoms persist. Retreatment might be necessary if lice are found or if eggs are observed at the hair-skin junction. If no clinical response is achieved to one of the recommended regimens, retreatment with an alternative regimen is recommended.

Management of Sex Partners

Sex partners within the previous month should be treated. Sexual contact should be avoided until patients and partners have been treated, bedding and clothing decontaminated, and reevaluation performed to rule out persistent infection.

Special Considerations

Pregnancy

Existing data from human participants demonstrate that pregnant and lactating women should be treated with either permethrin or pyrethrin with piperonyl butoxide. Because no teratogenicity or toxicity attributable to ivermectin has been observed during human pregnancy experience, ivermectin is classified as “human data suggest low risk” during pregnancy and probably compatible with breastfeeding.

HIV Infection

Persons who have pediculosis pubis and HIV infection should receive the same treatment regimen as those who do not have HIV.

Pubic (“crab”) lice most commonly are spread directly from person to person by sexual contact. Pubic lice very rarely may be spread by clothing, bedding, or a toilet seat.

The following are steps that can be taken to help prevent and control the spread of pubic (“crab”) lice:

• All sexual contacts of the infested person should be examined. All those who are infested should be treated.
• Sexual contact between the infested person(s) and their sexual partner(s) should be avoided until all have been examined, treated as necessary, and reevaluated to rule out persistent infestation.
• Machine wash and dry clothing worn and bedding used by the infested person in the hot water (at least 130°F) laundry cycle and the high heat drying cycle. Clothing and items that are not washable can be dry-cleaned OR sealed in a plastic bag and stored for 2 weeks.
• Do not share clothing, bedding, and towels used by an infested person.
• Do not use fumigant sprays or fogs; they are not necessary to control pubic (“crab”) lice and can be toxic if inhaled or absorbed through the skin.

Persons with pubic lice should be examined and treated for any other sexually transmitted diseases (STDs) that may be present.

What are pubic lice?

Also called crab lice or “crabs,” pubic lice are parasitic insects found primarily in the pubic or genital area of humans. Pubic lice infestation is found worldwide and occurs in all races, ethnic groups, and levels of society.

What do pubic lice look like?

Pubic lice have three forms: the egg (also called a nit), the nymph, and the adult.

Nit: Nits are lice eggs. They can be hard to see and are found firmly attached to the hair shaft. They are oval and usually yellow to white. Pubic lice nits take about 6–10 days to hatch.

Nymph: The nymph is an immature louse that hatches from the nit (egg). A nymph looks like an adult pubic louse but it is smaller. Pubic lice nymphs take about 2–3 weeks after hatching to mature into adults capable of reproducing. To live, a nymph must feed on blood.

Adult: The adult pubic louse resembles a miniature crab when viewed through a strong magnifying glass. Pubic lice have six legs; their two front legs are very large and look like the pincher claws of a crab. This is how they got the nickname “crabs.” Pubic lice are tan to grayish-white in color. Females lay nits and are usually larger than males. To live, lice must feed on blood. If the louse falls off a person, it dies within 1–2 days.

Where are pubic lice found?

Pubic lice usually are found in the genital area on pubic hair; but they may occasionally be found on other coarse body hair, such as hair on the legs, armpits, mustache, beard, eyebrows, or eyelashes. Pubic lice on the eyebrows or eyelashes of children may be a sign of sexual exposure or abuse. Lice found on the head generally are head lice, not pubic lice.

Animals do not get or spread pubic lice.

What are the signs and symptoms of pubic lice?

Signs and symptoms of pubic lice include

• Itching in the genital area
• Visible nits (lice eggs) or crawling lice

How did I get pubic lice?

Pubic lice usually are spread through sexual contact and are most common in adults. Pubic lice found on children may be a sign of sexual exposure or abuse. Occasionally, pubic lice may be spread by close personal contact or contact with articles such as clothing, bed linens, or towels that have been used by an infested person. A common misconception is that pubic lice are spread easily by sitting on a toilet seat. This would be extremely rare because lice cannot live long away from a warm human body and they do not have feet designed to hold onto or walk on smooth surfaces such as toilet seats.

Persons infested with pubic lice should be examined for the presence of other sexually transmitted diseases.

How is a pubic lice infestation diagnosed?

A pubic lice infestation is diagnosed by finding a “crab” louse or egg (nit) on hair in the pubic region or, less commonly, elsewhere on the body (eyebrows, eyelashes, beard, mustache, armpit, perianal area, groin, trunk, scalp). Pubic lice may be difficult to find because there may be only a few. Pubic lice often attach themselves to more than one hair and generally do not crawl as quickly as head and body lice. If crawling lice are not seen, finding nits in the pubic area strongly suggests 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. Persons infested with pubic lice should be investigated for the presence of other sexually transmitted diseases.

Although pubic lice and nits can be large enough to be seen with the naked eye, a magnifying lens may be necessary to find lice or eggs.