Pubic lice (Sing: pubic louse), also known as crab louse, crabs, or Fullers; Latin name Pthirus pubis are tiny parasitic blood-sucking wingless insects that infest the human genitals, causing itching and red spots.
The only other animal known to be affected by this insect is the gorilla. Crabs may also affect other coarse hair on the body, including the eyelashes, eyebrows, beards, mustaches, as well as the hair on the back and abdomen. Pubic lice are about 2mm long and are gray-brown in color.
Pubic lice pass from person-to-person, in most cases as a result of sexual intercourse - close hugging and kissing are also possible routes.
Parents can pass on the lice to their children via the sharing of towels, clothing, bedding or closets (wardrobes); however this is rare. Infested children are at risk of lice spreading to their eyelashes, resulting in possible infections.
Crabs affect sexually active adolescents and adults much more commonly than children. Pubic lice cannot survive for very long away from the warmth and humidity of a human body. Experts say that crabs are the most contagious STD (sexually transmitted disease).
If an infected person has sexual intercourse with a non-infected person, the latter has a 90% risk of getting an infestation, according to The Mayo Clinic.
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You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Here are some key points about crabs. More detail and supporting information is in the main article.
- There are approximately 3 million cases of crabs in the US each year.
- Having pubic lice does not necessarily mean that an individual has poor hygiene.
- The most common symptom of crabs is itching.
- Pubic lice can spread to other parts of the body covered in hair, including chests, beards and eyelashes.
- Crabs are commonly spread through sexual contact.
- Wearing a condom does not help prevent the spread of pubic lice.
- Nonsexual transmission of crabs is also possible, through contact with infested materials.
- Pubic lice can often be diagnosed with the naked eye.
- Children aged below 18 and pregnant women should discuss treatment with health care providers.
- Clothes and bedding should be washed in hot water to remove pubic lice.
Symptoms of pubic lice infestation
A symptom is something the patient feels and reports, while a sign is something other people, such as the doctor detect. For example, pain may be a symptom while a rash may be a sign.
Signs and symptoms may not become apparent until one to three weeks after a person comes into contact with the lice. Signs and symptoms may include:
- Itching in the pubic region - this is not caused by biting from the insect, but from an allergic reaction to the louse saliva and feces (droppings, excrements, stools). The itching is usually worse at night
- Red spots and skin lesions - small red bumps or spots may appear. Scratching by the patient may also results in marks
- Blue spots on the skin - especially on the thighs or lower abdomen
- Other parts of the body - the lice may spread to the stomach, upper thighs, chest, mustache, and beard. In children they may spread to the eyelashes. Wherever the lice are located, symptoms of itching are common, as well as skin irritation
- Louse droppings - the presence of dark brown or black powder on the skin or in underwear could indicate the presence of crab droppings
- Blood in underwear - this is usually caused by scratching by the patient which breaks the skin
- Adult pubic lice and eggs - an adult pubic louse is smaller than a match head; it is approximately 2mm long. It has six legs and has a gray-brown color. Its back legs are very large, and look like the claws of a crab. The large back legs are used to cling onto the hair.
Symptoms of pubic lice include itching, skin lesions and the presence of louse eggs.
Eggs are very small, oval shaped, with a yellowish-white color. They stick firmly to the base of the hair.
Both the adult pubic lice and their eggs are visible to the naked eye - some people may need a magnifying glass. You may be able to detect them in coarse hair in the following parts of your body:
- Along the edge of the scalp
- In facial hair (beards, mustaches)
- In the eyebrows
- In the eyelashes
- In the hair around the anus
- In the hair of the armpits
- In the pubic hair (genital area).
The detection of empty eggshells (nits) after treatment does not mean the infestation is necessarily still present.
If complications to occur they tend to be minor and usually as a result of leaving the infestation untreated.
Skin - intense itching can lead to scratching, which can cause excoriation (skin flakes off) and/or infection.
Eyes - if the eyelashes have been affected there is a risk of:
- Blepharitis - swelling of the eyelids. The patient will have a foreign body or burning sensation, there may be excessive tearing (liquid tears), itching, photophobia (sensitivity to light), red and swollen eyelids, the whites of the eyes becomes reddened, blurred vision, or crusting of the eyelashes first thing in the morning.
- Conjunctivitis - there is a thin layer of cells (membrane) between the inner surface of the eyelids and the whites of the eyes, called the conjunctiva. Conjunctivitis is when the conjunctiva becomes inflamed. Another name for conjunctivitis is pink eye. Inflammation causes tiny blood vessels (capillaries) in the conjunctiva to become more prominent, giving the eye a red or pink look.
- Corneal epithelial keratitis - the cornea becomes inflamed.
When should you see your doctor?
In the majority of cases OTC (over-the-counter, no prescription required) medications will successfully treat the infestation. You should see you doctor if:
- The OTC medication, usually in the form of a lotion, cream or shampoo, does not kill the lice
- You are pregnant - pregnant women should not use anti-lice medications without checking with their doctor
- You have developed a skin infection due to skin lesions (from scratching)
- The patient is a child.
Causes of pubic lice infestation
An infested person needs to be in close-body contact with another person for the infestation to be passed on. Crabs cannot jump, fly or swim - they crawl from one hair to another.
- Sex - the most common form of contact that results in an infestation is through sex, including sexual intercourse, anal sex and oral sex
- Non-sexual bodily contact - such as hugging or kissing may also result in an infestation (less common)
- Sharing items - sharing towels, bedding, etc., with an infected person can raise the risk of pubic lice infestation in other people (much smaller risk).
Condoms are effective for protection against many sexually transmitted infections, but not from pubic lice infestation. It is not the penetration during the sexual act that raises the risk, but rather the close proximity of hair from one person to the hair of another person.
Risk factors for pubic lice
A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2.
Risk factors for crabs include:
- Being sexually active, especially for adolescents
- Having several sex partners
- Having sexual relations with a person who has an infestation
- Sharing towels, bedding or clothing with an infested person.
Backpacking, sightseeing and rest and relaxation vacations to tropical destinations or European countries are perceived by American women as ideal settings for sex with both steady and casual sexual partners, according to the findings of a new study.
Young men with detectable levels of the human immunodeficiency virus who have sex with men are more likely to have anal sex without a condom, including sex with a partner who does not have the virus, according to research published in JAMA Pediatrics.
Pubic lice life cycle
A pubic louse has a life expectancy of between 1 to 3 months. A female might lay up to 300 eggs during her life.
Eggs hatch within 6-10 days. Lice take 2-3 weeks to reach maturity (the age for reproduction).
A louse can survive for up to 24 hours away from the human body. They will never deliberately leave a human, unless it is to crawl onto another human, because they feed on human blood - without it they starve. The only other animal, apart from humans, known to be affected by pubic lice infestation is the gorilla.
Tests and diagnosis for pubic lice
Pubic lice can be detected through visual examination - a magnifying glass or microscope can often help.
Both the doctor, as well as the patient can easily detect the presence of lice and eggs through a visual examination of the affected area - usually the pubic area. Some people may find that a magnifying glass is easier.
An infestation is confirmed if moving lice are spotted.
The presence of lice eggs (nits) does not necessarily mean there is an infestation. After successful treatment there may still be some remaining empty egg shells.
Sexually transmitted infections - doctors in the UK and many other countries will ask the patient whether the infestation was transferred through sexual contact or some other means. If they were the result of sexual contact the doctor will recommend that the patient be screened for other STIs (sexually transmitted infections) or STDs (sexually transmitted diseases) as a precaution.
In this text, and virtually all medical texts, STI and STD have the same meaning.
Treatments for pubic lice
Crabs can be treated without needing to go to see a doctor. There are insecticidal creams, lotions and shampoos available at pharmacies which do not require a doctor's prescription. Ask your pharmacy for a suitable medication. If you are pregnant, see your doctor first.
Most treatments are applied once, and then again seven days later.
People with pubic lice should avoid close physical contact with others and make sure any who have come into contact with them seek treatment.
Anybody with an infestation should also make sure that other people who came into close physical contact receive treatment; including all members of the household, not just sexual partners.
Some pubic lice may have developed resistance to some medications - i.e. the medication does not work because they have become immune to it. If this happens to you, either talk to a pharmacist or your doctor - they will recommend an alternative treatment after checking whether you have been applying the application properly.
Make sure you talk to your pharmacist or GP before using a treatment so that you know how to use it properly. Follow their instructions carefully. Sometimes the GP's or pharmacist's instructions may vary from what is written on the packet; do what the health care professional told you - if their instructions vary from what is written on the packet, do not be afraid to mention this fact to them.
The following groups of people should not be treated without first talking to your doctor or qualified pharmacist (do not be afraid to ask the person at the pharmacy whether they are fully qualified pharmacists):
- Children under 18 years of age
- A pregnant woman.
Over-the-counter (OTC) lotions and creams - these are usually the first line of defense. If they do not kill the lice a doctor may prescribe a stronger lotion (or shampoo).
- Malathion (Ovide) aqueous lotion - this medication is suitable for anybody aged over six months. Malathion is flammable (can catch fire), so keep away from cigarettes, hair dryers and other heat sources. In many countries this is a prescription lotion
- Permethrin 5% dermal cream - this medication should not be used on patients aged less than 18 years. Pregnant women and breastfeeding mothers should not take it, unless her doctor says so.
Instructions for both malathion lotion or permethrin cream, in most cases, are:
- Apply the lotion to the whole body, including the scalp, face, neck and ears (not just the affected areas)
- Make sure the lotion is applied to the eyebrows
- Apply the lotion to your beard or mustache (if you have a beard or mustache)
- Apply to pubic hair, hair between your legs, and hair around the anus
- Keep the lotion away from your eyes. If some does get in your eyes, rinse thoroughly with water
- One total application will generally require about 100ml of lotion or 30-60g of cream
- Malathion lotion - leave on for 12 hours or overnight
- Permethrin 5% cream - leave on for 24 hours
- Wash the medication off with warm water (gently and thoroughly)
- Repeat the whole process seven days later
- Do not use medication more often than indicated - do not repeat the application for more than three consecutive weeks.
Eyelash treatment - anybody with an eyelash infestation should treat the eyelashes and the body as well. Patients should not try to pull the nits out - there is a serious risk of eye injury. The medication for eyelashes is different from the treatments for other parts of the body - do not use them on your eyes. For eyelashes you should use:
An eye ointment - ideal for patients under 18 years of age and pregnant or nursing mothers. The medication has a white or yellow soft paraffin base and suffocates the parasite.
- Apply twice a day to the eyelashes, making sure every part of each eyelash is covered
- Wash hands thoroughly before applying, and again afterwards
- Each time the ointment is applied, gently wipe away any ointment that is still there from the previous application (with a tissue). Then throw away the tissue
- Continue like this, twice a day for eight days. If lice are still present (ignore the eggs) continue until day 10.
An insecticide shampoo or cream rinse - for example, permethrin 1%.
- Apply the cream to where the eyelashes start (the base), using a cotton bud
- Do not open your eyes during the application
- Leave it there for 5 to 10 minutes
- Wash off the cream with water
- If any gets into your eyes wash them straight away with water.
In the majority of cases, the first treatment will be successful and all the lice will be killed off. However, the eggs may still be there, with the risk of hatching. If you re-apply the medication after seven days it makes sure that any hatched lice will be killed off before they are mature enough to reproduce.
If you have an infestation, do not share bedding, clothing or towels with other people.
One week after your second treatment check for lice again. If you are not sure how to check, go to your GP (general practitioner, primary care physician) or a GUM (genitor-urinary medicine) clinic.
Nits (eggs or empty egg-shells) may linger for a while even after successful treatment. Their presence does not mean the infestation is still there. However, if you find moving lice or eggs that are not empty (they can hatch), you should see your GP.
You doctor will make sure the patient fully understands how to apply the medication. In some cases the GP may ask the patient to repeat the treatment. If treatment fails a second time the doctor will recommend an alternative medication. This may mean switching from malathion to permethrin, or vice-versa. Other possible medications include phenothrin or carbaryl.
Preventing pubic lice
Protecting others - if you have an infestation, refrain from sexual activity until your treatment is completed successfully.
Sexual partners - the fewer sexual partners you have, the lower the risk will be of becoming infected with STIs generally, including crabs.
Regular check-ups - regular check-ups can reduce the risk for all STIs.
Condoms - although condoms will not protect you from pubic lice, they will help protect you from other STIs.
Sharing items - if you have an infestation, do not share your bedding, clothing, towels and closet with other members of your household.
Other members of the household - if one person has an infestation, treat everyone in that household for pubic lice as a precaution.