What Are Pubic Lice

  • Suruthy MaryBachelor in Biomedical Science (IBMS)- BSc in University of Portsmouth, UK

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Introduction

Pubic lice, also known as ‘Crab lice’ or ‘Crabs’, are non-serious but unpleasant parasites that spread through close physical contact. In this article, we will discuss how to identify pubic lice, understand their symptoms, seek treatment, and prevent their transmission.

Pubic louse biology

Despite being known as ‘crabs’, pubic lice (known scientifically as ‘Phthirus pubis’) are insects which feed on the blood of warm-blooded hosts. Pubic lice are not the only lice found in humans and are related to head and body lice. These lice are specific to humans and are specially adapted to survive on humans as a host. When dislodged from their host, pubic lice typically die within 2 days.

Infestation with pubic lice is medically known as ‘phthiriasis’, and millions of cases occur worldwide each year. It can be found equally in all individuals, regardless of gender, ethnicity or economic status. However, it is more commonly seen in adults as sexual contact is the main way pubic lice spread.

Appearance

The adult lice are very small, only around 1.1- 1.8mm long, and are tan or greyish-brown. Unlike other lice, they have round, flat bodies and the two front legs are much larger than the others, resembling a crab's claws, hence the name.

Because of their small size, lice tend to inhabit specific areas of the body. In the case of pubic lice, this is usually in the pubic hair and around the genital region, though they may also be found on the armpits, face or chest.

Lifecycle

Like all lice, pubic lice can only survive as parasites, spending their whole life living on their host. Pubic lice have three stages in their lifecycle: eggs (aka. ‘nits’), nymphs and adults.

Eggs take anywhere between 6 and 10 days to hatch into the nymph stage. Nymphs look the same as the adults, but smaller. They take up to 3 weeks to reach maturity, at which point they can reproduce.

During this time, the nymphs feed on blood regularly to gain the nutrients they need to grow. The females usually grow larger and will start laying eggs as soon as they mature, producing around 30 eggs in their short lifespan of one month.4

Transmission

Pubic lice can’t fly or jump to new hosts but can climb onto people. Pubic lice are transmitted through close body contact, primarily during sexual activities, but can also spread via fabrics (e.g. bedding, towels, clothes), though this is less common.

Symptoms

Many cases of pubic lice don’t have any symptoms and are first noticed when the lice or their eggs are directly seen. Common symptoms include genital itching, typically more pronounced at night. The itching is caused by an allergic reaction to the louse’s saliva.

Complications

Pubic lice can’t transmit disease, though scratching at the bites can break the skin barrier and cause a bacterial infection such as impetigo or pyoderma.

If left untreated the skin may become discoloured and itching may become more severe.2 In rare cases where the eyelashes are involved, conjunctivitis (eye inflammation) or blepharitis (inflammation of the eyelids) may develop.

Diagnosis

Physical examination

Pubic lice can be difficult to spot due to their small size and the fact there may be only a few of them, though the adults or their eggs can be seen with the naked eye. Unlike other lice, they move quite slowly and look distinct from hair and body lice.

If you experience itching and notice eggs or bites, pubic lice are likely present.

The eggs can be hard to see - they are usually white or yellow with an oval shape and are found stuck to hairs. The bites typically appear as small blue or red marks on the skin. Dark red or brown spots in the underwear can also indicate that pubic lice are present, as these marks are their droppings.2

If you observe any of these symptoms and suggest you may have pubic lice, a doctor or nurse at a local surgery or sexual health clinic will be able to confirm this. They may use a comb or magnifying lens to inspect potentially affected area.2

Medical history

You may be asked about previous sexual partners and activity as this is important in preventing outbreaks of pubic lice. In the event pubic lice are found, you will likely be asked to undergo further STI testing.1

Similar conditions

Body lice, head lice and scabies may cause similar symptoms to pubic lice. Fungal skin infections may also cause similar itching symptoms and discolouration. If in doubt, always seek medical advice.

Treatment

It is important to seek treatment for pubic lice, as they will not go away by themselves. Both over-the-counter and prescription options are available for treating pubic lice.

You do not need a prescription for many readily available lice-killing lotions or shampoos, most of which use permethrin (a mild insecticide) as the active ingredient. It is important that the whole body is treated and instructions are closely followed. If using lotions, they should be left on for the recommended time before washing as this may rinse off the medication and make it less effective. It’s important to change into clean underwear and clothing after treatment.

It's crucial to ensure that recent sexual partners or individuals with close contact also receive treatment, regardless of whether they have symptoms. The main cause of treatment failure is not following the medication instructions or following a complete course of treatment. You may be asked to return to a clinic to check whether treatment has worked.2

It is possible for lice to develop resistance to permethrin, in which case prescription medications may be given as an alternative treatment. However, these should not be used as an initial treatment due to the increased risk of side effects.

Shaving is not an effective way of removing pubic lice, as they can survive even on very short hairs.2

Prevention

Prevention of pubic lice is difficult. The only reliable way to reduce the risk is to limit the number of people you have sexual or other close contact with or to ensure any partners have already undergone STI screening, or completed any courses of treatment for pubic lice. Condoms are recommended for all sexual activities to reduce the risk of contracting other STIs. However, they will not prevent pubic lice from spreading.2

To ensure that treatment is successful and that pubic lice don’t spread, it is important to wash bedding and clothes at 50°C or dry clean them. If the fabrics aren’t suitable for washing or dry cleaning, they can be stored in a sealed plastic bag for a week to ensure all lice have died. Vacuuming mattresses can also help to remove lice. Clothes or bedding should not be shared whilst undergoing treatment, and neither should grooming products such as razors.

Any close contact should be avoided until treatment has finished.2 Fumigation is not needed to treat pubic lice as there are many effective ways of removing pubic lice from the environment that don’t involve a risk of inhaling or absorbing toxic sprays or fogging agents.2

Summary

Pubic lice, also known as "crabs," are tiny parasitic insects that infest pubic hair and sometimes other coarse body hair. They spread through close physical contact and can cause itching and discomfort. Treatment involves over-the-counter or prescription medication to kill the lice and their eggs, along with thorough hygiene practices.

References

  1. Bragg BN, Wills C. Pediculosis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Feb 23]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK470343/
  2. Khan T. Phthiriasis palpebrarum presenting as anterior blepharitis. Indian Journal of Public Health [Internet]. 2018 Sep [cited 2024 Feb 23];62(3):239. Available from: https://journals.lww.com/ijph/fulltext/2018/62030/phthiriasis_palpebrarum_presenting_as_anterior.17.aspx

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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George Yates

BSc Zoology – University of Bangor, Wales

George is a researcher currently working in the medical diagnostics industry. His work is focused on infectious disease microbiology and molecular biology, and he also has several years of experience in the food safety, pharmaceutical and biotechnology industries.

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