Crabs (Pubic Lice)

Reviewed on 5/27/2022

What Are Crabs (Pubic Lice) (Picture)?

Picture of pubic louse (crab).
Many people who have crabs, experience itching that worse at night.

"Crabs" is the common term for lice found in the pubic hair of humans. Crabs is a parasite infection medically known as Pediculosis pubis or pubic lice. Barely the size of a pinhead, lice are organisms that live only with the help of another organism, called a host. There are thousands of types of lice, some of which have developed an attraction to humans.

The official name for the organism responsible for pubic lice is Pthirus pubis. Other lice that often infect humans are Pediculus humanus capitis (head lice) and Pediculus humanus corporis (body lice). The term "crabs" seems to come from the microscopic appearance of the pubic louse. The pubic lice organisms are visible to the naked eye in affected areas. The lice are typically seen attached to hair in public areas but may sometimes appear in other areas of the body where coarse hair is present (such as beard, chest, armpits, etc.).

The pubic louse is distinct morphologically (somewhat rounded with three pairs of legs on either side of the body from which it takes its descriptive name) from the head and body louse. The female lifespan is slightly shorter (three weeks), and she produces fewer eggs per day (three) than her counterparts. The eggs attach to the base of the pubic hair shaft for approximately six to eight days before hatching.

What Are the Symptoms of Crabs (Pubic Lice)? What Body Areas Do They Infest?

You may have crabs if you have the following symptoms:

  • Itching and burning of the pubic area
  • Itching that may spread to other moist areas of the body such as the armpit
  • Itching that is worse at night
  • Intense or prolonged scratching that may lead to skin injuries that may become infected by bacteria

What Causes Crabs (Pubic Lice) (Transmission)?

The source of infection for pubic lice is intimate contact with an infected person or contaminated objects:

  • Since transmission occurs during intimate contact, sexual intercourse is not necessary for the spread of pubic lice; however, they are not a sexually transmitted disease (STD).
  • Pubic lice can also be transmitted by contact with contaminated belongings such as towels, bed sheets, or clothing. Lice do not jump or fly, so direct contact is necessary for transmission. An individual may acquire an infection by sharing bedding or towels.
  • Cats, dogs, and other pets are not involved in the spread of human lice. Your pet cannot become infected with human lice and transmit the lice to another person.

What Remedies and Medications Treat Crabs (Pubic Lice) and Kill Them?

Generally, pubic lice can be cured with an application of certain medications, but in some circumstances, it may be necessary to seek a doctor's care. Go to a doctor immediately if you think you may have an infection.

  • One of the main concerns with pubic lice is that people often scratch incessantly, and this scratching can lead to a secondary bacterial infection.
  • When scratching is intense for long periods, the skin can become broken.
  • If you notice a large area of redness or pus in the area, you may have a skin infection.
  • Other signs of a pubic infection include a fever, burning when you urinate, or genital discharge.

Medications that can be used to treat crabs include the following:

  • Permethrin (Elimite) is a lice-killing product that is available over the counter (OTC) without a prescription. When using this product it is important to exactly follow the instructions on the package.
    • Avoid mucous membranes, which are found at the tip of the penis and the opening of the vagina.
    • Repeat anti-lice treatment in seven to 10 days to kill nits that may have hatched.
  • Lindane (Kwell) is an alternative treatment when permethrin (Elimite) is not available. Lindane requires a doctor's prescription.
    • Apply for 10 minutes then rinse with warm water.
    • Lindane should not be used on children. Lindane can be toxic to the brain and nervous system and should only be used when other treatments have failed.
  • Malathion lotion (Ovide) and ivermectin (Stromectol) are other prescription medications that have been shown to be effective against pubic lice or crabs.
  • Diphenhydramine (Benadryl) and other over-the-counter antihistamines can be used for itching.

When Should You Call a Doctor for Crabs (Pubic Lice)?

Pubic lice are generally harmless, but people with sexually transmitted infections often have multiple infections, and other sexually transmitted infections that can be more dangerous.

  • If the patient has been to the emergency department, they will probably be asked to follow-up with their regular doctor.
  • If a patient has treated themselves for crabs, consider a visit to the doctor as part of follow-up care.

Can You Cure Crab (Pubic Lice) Infections?

If untreated, itching and symptoms will continue. Eventually, everyone within close contact with the infected individual will become infected and develop symptoms.

  • If medication, combing, and hygiene are used properly, the infection should clear.
  • Be wary of re-infection. Continued contact will reintroduce the infection even after the home care measures are taken.

Can You Prevent Crabs (Pubic Lice)?

Crabs are usually spread by direct skin-to-skin intimate contact.

  • Avoid contact with known infected people and textiles or clothing that may have been contaminated by someone who is infected with pubic lice.
  • To avoid spreading the lice, a person with crabs should not have close or intimate contact with anyone else until the infestation has been fully treated.
  • After treatment has been completed, ensure that all clothing and linens have been disinfected to avoid re-infection or spread of the infection to someone else in the home.

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Reviewed on 5/27/2022
Goldstein, Adam O, MD, MPH, and Beth G Goldstein, MD. "Patient Education: Pubic lice (Beyond the Basics)." UpToDate. Jan 2020.