What Are Pubic Lice (Crabs)?

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Pubic lice (Phthirus pubis)—more commonly known as crabs—are parasitic insects that feed on human blood. They are notorious for infesting pubic hair, but can also be found on facial hair, the hair of armpits, and even on eyebrows and eyelashes.

They derive their name from their crab-like appearance. They are small, but you may be able to see them with the naked eye.

Pubic louse

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Typically spread through sexual contact, the insects can only survive for a short period of time away from the warmth and humidity of the human body. The infestation, referred to as pediculosis pubis, can be treated with over-the-counter or prescription drugs that get applied to the skin.

Pubic lice are not the same thing as head lice. Head lice involve a different type of insect, named Pediculus humanus capitis, that is more easily transmitted through casual contact.

Pubic Lice Symptoms

Itching is the signature symptom of pediculosis pubis. Despite what some think, the itching is not caused by the insect bite, per se. Rather, it's a result of a hypersensitive reaction to the parasite's saliva.

As the population of lice and duration of the infestation grows, so does the intensity of the itching.

Some infestations cause bluish or grayish macules, tiny splotches on the skin that are neither raised nor depressed.

Adult lice can sometimes be spotted crawling on the body. They vary in color from a grayish-white to tannish-brown.

Lice may be found on hair of the:

  • Genital area (most common)
  • Legs
  • Armpits
  • Mustache/beard
  • Eyebrows and eyelashes

Causes

You get crabs by being in close physical contact with someone who already has them. Sexual contact is by far the most common mode of transmission. You can also get them from the towels, bedsheets, or clothing of an infested individual.

The crabs go through various stages in their life cycle. Once they are transmitted, they will begin to lay eggs, called nits, on the shafts of hair. The whitish, oblong-shaped eggs will incubate for six to 10 days before hatching.

The immature lice, known as nymphs, will take between two to three weeks to fully mature, wherein they are capable of reproducing and laying more eggs.

Female crabs are usually larger than males and can lay around 60 eggs in their three- to four-week life span.

To live, the crabs must feed on blood. The lice can only survive for between 24 and 48 hours away from the human body.

Unlike head lice, fomites (like bedding or clothes) only play a minor role in the transmission of crabs.

Despite popular belief, you cannot get crabs from public toilet seats or pets.

Diagnosis

A case of public lice can be diagnosed by inspecting the infested hair. Adult crabs are very small—around 2 millimeters (0.08 inches)—but can often be seen during a physical exam.

However, because of their coloring, the lice can blend in with some people's skin tone. In addition, there may only be a few, which means they can be harder to find.

A magnifying glass can help a practitioner spot lice if they are not immediately apparent. When using one, it's easier to see each louse's six legs. The front two are very large and look like the pinchers of a crab.

Upon close inspection, you may see faint bluish macules where the lice have bitten you.

If you are unable to spot them or are unsure what you are looking at, go to the healthcare provider or STD clinic for an examination immediately. A snipping of your pubic hair may be taken and examined under the microscope to make a definitive diagnosis.

People diagnosed with crabs should be screened for sexually transmitted infections.

Treatment

There are a number of topical (applied to the skin) medications used to treat pediculosis pubis.

Permethrin 1% cream rinse is an effective over-the-counter drug that can usually resolve the infestation with one treatment.

Pyrethrin with piperonyl butoxide is another effective topical medication.

With that said, lice can sometimes develop a resistance to permethrin or pyrethrin, particularly in populations where pediculosis pubis is widespread. That means that while the drug used to be effective, the lice have developed a way to survive it over time.

Malathion 0.5% lotion is a prescription medication that can be used when treatment failure due to resistance is suspected. Treatment with oral ivermectin is another option, which should be repeated after seven to 14 days.

Note: Lindane 1%, a prescription lotion, was once used to treat public lice in certain adults. It is no longer recommended due to toxicity and other concerns.

How to Use Topical Treatments

The application of anti-lice lotions and shampoos involve similar steps:

  1. Wash and dry the affected areas thoroughly.
  2. Follow the instructions in the package or on the label; thoroughly cover the infested area with the medication.
  3. Leave the lice medication on for the recommended amount of time.
  4. Remove the medication by carefully following the instructions on the package.
  5. Use a fine-tooth comb (provided with the medication) or your fingernails to remove dead lice and nits still clinging to hair shafts.

Care should be taken when treating eyelash lice, as the recommended shampoos and lotions should not be applied to the eye area. Instead, an eye ointment or petroleum jelly should be applied to the edge of the eyelids two times a day for 10 days. Follow your healthcare provider's specific advice.

If the first treatment fails to provide relief, a second may be needed in three to seven days. If lice still persist, call your healthcare provider.

Other Measures

You do not need to shave your pubic (or other) hair. As long as you follow the medication instructions completely, you should not have any problem clearing the infestation.

All bedding, towels, and used clothing should be thoroughly washed and dried on the hottest temperature setting. Any items that cannot be laundered or dry-cleaned should be stored in a sealed plastic bag for two weeks to kill any remaining insects.

Until the infestation is fully resolved, avoid intimate contact of any sort.

Crabs are not a reportable health concern, but you should advise your sex partners if you've been diagnosed so that they can be treated for pubic lice and screened for sexually transmitted infections.

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3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Pubic "crab" lice: Frequently asked questions.

  2. Workowski KA, Bachmann LH, Chan PA, et al. Sexually transmitted infections treatment guidelines, 2021MMWR Recomm Rep. 2021;70(4):1-187. doi:10.15585/mmwr.rr7004a1

  3. Centers for Disease Control and Prevention. Sexually Transmitted Infections and Treatment Guidelines, 2021. Morbidity and Mortality Weekly Report, Vol. 70, No. 4.

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