Pubic lice, also known as crab lice or crabs, are tiny, parasitic insects that feed on blood. They spread easily and affect the human genitals, causing itching and red spots.
Apart from the genital area, crabs may also affect other coarse hair on the body, including the eyelashes, eyebrows, a beard, mustache, and any hair on the back and abdomen.
Lice are visible to the naked eye. They are about 2 millimeters (mm) long, and they are gray-brown in color.
They pass from one person to another, usually as a result of sexual intercourse, but also through close hugging and kissing.
More rarely, they can be passed on by sharing towels, clothing, bedding, or closets. Children can catch them in this way. In children, lice can affect the eyelashes, resulting in possible infections.
However, they are more common in sexually active adolescents and adults, and they are considered the most contagious sexually transmitted infection (STI). A person with lice has a high chance of passing on the lice to a sexual partner.
They affect around 3 million people each year in the United States.
Lice, or crabs, can be treated using over-the-counter (OTC) preparations. Insecticidal creams, lotions, and shampoos are available without prescription at pharmacies. The pharmacist will suggest a suitable medication. During pregnancy, it is important to see a doctor first.
Most treatments are applied once, and then again 7 days later, if lice are observed.
Anybody who has lice should avoid close physical contact with other people until the lice are gone. Anyone who has been in close contact with the person should receive treatment. This usually means sexual partners.
Some lice have developed a resistance to some medications. If a medication does not work, first check that you have applied it correctly, then speak to a pharmacist or doctor about an alternative treatment.
Before using a treatment, check with a pharmacist or doctor that you know how to use it, and follow their instructions carefully.
If OTC medications do not kill the lice, a doctor may prescribe a stronger lotion or shampoo.
- Ivermectin lotion is approved for management of pubic lice. Oral ivermectin has been successfully used to treat pubic lice, but this has not been approved by the FDA.
- Malathion (Ovide) aqueous lotion is suitable for anybody aged over 6 months. Malathion is flammable, so it must keep away from cigarettes, hair dryers, and other heat sources. However, it has not been approved as a treatment for pubic lice in the United States by the Food and Drug Administration (FDA).
Instructions for malathion lotion or ivermectin cream, in most cases, are:
- Apply the lotion to the whole body, including the scalp, face, neck and ears, as well as the affected areas only.
- Keep the lotion away from the eyes. If some does get in the eyes, rinse thoroughly with water.
- One total application will generally require about 100ml of lotion or 30 grams (g) to 60 g of cream.
- Ivermectin lotion: Leave on for 10 minutes
- Malathion lotion: Leave on for 12 hours or overnight.
- Wash the medication off with warm water, gently and thoroughly.
- Comb hair with a fine tooth comb to remove lice eggs.
- Repeat the process 7 days later.
- Do not use the medication more often than indicated, and do not repeat the application for more than 3 consecutive weeks.
Lindane shampoo is a prescription drug that can kill lice and eggs, but it is not the first treatment doctors will give, as it can be toxic to the brain. Anyone weighing less than 110 pounds, people who have seizures, women who are pregnant or breastfeeding, and those with irritated skin or sores should not use it.
If the eyelashes are affected, treat the whole body as well as the lashes. Do not try to pull the eggs or shells out, as there is a risk of eye injury.
The medication for eyelashes is different from the treatments for other parts of the body. Those should not be used on the eyes.
If only a few lice or nits are noted, they can be removed by fingernails or by a fine tooth comb.
An eye ointment is available for those aged under 18 years or during pregnancy and breastfeeding. It has a white or yellow, soft paraffin base, which suffocates the parasite.
- Apply twice to four times a day to the eyelashes, making sure every part of each eyelash is covered.
- Wash hands thoroughly before applying, and again after.
- Each time the ointment is applied, gently wipe away any ointment that is still there from the previous application. Use a tissue, then dispose of it.
- Apply twice to four times a day for 8 days. Continue treatment until dayt 10 if lice, but not eggs, remain.
Another option is a weaker insecticide shampoo or cream rinse, for example, permethrin 1 percent.
- Keeping the eyes closed, apply the cream to the base of the eyelashes start, using a cotton bud.
- Leave for 5 to 10 minutes.
- Wash off with water.
- If any gets into the eyes, rinse them straight away with water.
In most cases, the first treatment will successfully kill all the lice.
However, the eggs may remain, with the risk of hatching. Re-applying the medication after 7 days ensures that any hatched lice are killed off before they are mature enough to reproduce.
One week after the second treatment, check for lice again. A health provider can help you do this.
Nits, which are eggs or empty egg-shells, may remain for a while even after successful treatment. This does not mean the infestation is still there. However, if there are moving lice or eggs that are not empty, they may be able to hatch. In this case, see a doctor.
- Itching will occur in the pubic region, not when the insect bites but because the bite will trigger an allergic reaction to the louse saliva and feces. The itching is usually worse at night.
- Red spots and skin lesions will appear, usually as small red bumps or spots. Scratching may also result in marks.
- Blue spots on the skin may be visible on the thighs or lower abdomen.
- Other parts of the body may show symptoms, such as the stomach, upper thighs, chest, mustache, and beard.
- Children may have symptoms around the eyelashes.
- Louse droppings may appear as dark brown or black powder on the skin or in underwear.
- Blood may be seen in underwear, usually as a result of scratching, which breaks the skin.
Will I see the lice?
The lice may be visible to the naked eye.
An adult pubic louse is around 2mm long. It has six legs and gray-brown color. Its back legs are large and look like the claws of a crab. These large back legs are used to cling onto the hair.
Eggs are very small, oval-shaped, with a yellowish-white color. They stick firmly to the base of the hair.
The signs of lice may be visible in coarse hair:
- along the edge of the scalp
- in facial hair, such as a beard or mustache
- in the eyebrows
- in the eyelashes
- in the hair around the anus
- in the hair of the armpits
- in the pubic hair, around the genital area
After treatment, empty eggshells may remain. This does not mean the infestation is necessarily still present.
Close body contact with another person is needed for lice to be passed on. They cannot jump, fly, or swim, but they crawl from one hair to another.
Here are some common ways of passing on lice:
- any type of sexual activity
- non-sexual bodily contact, such as hugging or kissing, but this is less common
- sharing towels, bedding, and other personal items
Condoms do not protect against a pubic lice infestation. It is the proximity of body hair that enables them to move.
Risk factors include:
- being sexually active, especially adolescents
- having several sex partners
- having sexual relations with a person who has an infestation
- sharing towels, bedding, or clothing
A pubic louse lives for between 1 and 3 months. A female might lay up to 300 eggs during her lifetime.
Eggs hatch within 6 to 10 days. Lice take 2 to 3 weeks to reach maturity, the age for reproduction.
A louse can survive for up to 24 hours away from the human body. Lice will never deliberately leave a human, except to crawl onto another human, because they feed on human blood. Without blood, they starve.
Apart from humans, only the gorilla is known to be susceptible to pubic lice.
In most cases, OTC medications will successfully treat the infestation.
Medical help is needed if:
- OTC medication does not kill the lice
- a woman has lice during pregnancy, because the OTC treatment may not be suitable
- a skin infection results from scratching
- the patient is under 18 years of age
Without treatment, complications can arise.
Scratching can cause skin to flake off and increases the risk of a skin infection.
If the eyelashes are affected there is a risk of inflammation and infection, for example:
If treatment does not work
In most cases, one round of treatment will successfully kill all the lice.
However, a second treatment is needed to kill lice that hatch after the first application. One week after the second treatment, check for lice again.
Nits, which are eggs or empty egg-shells, may remain for a while even after successful treatment. This does not mean the infestation is still there. A health provider can help you check.
If signs of the infestation remain, for example, moving lice or eggs that are not empty and could still hatch, see a doctor. Stronger medication may be needed.
Lice and eggs are easy to detect through a visual examination of the affected area. A magnifying glass may help.
An infestation is confirmed if moving lice are spotted.
The presence of eggs does not necessarily mean there is an infestation. After successful treatment, some empty egg shells may remain.
The doctor may recommend screening for other STDs, as a precaution.
Some tips can help prevent lice.
Protect others if you have an infestation. This involves refraining from sexual activity until your treatment is completed successfully, and not sharing towels or other personal items. If one person has lice, treat sexual partners as a precaution.
Avoid having multiple sexual partners, as this increases the risk.
Have regular check-ups, to reduce the risk of lice and other all STIs.
Condoms offer protection from some STDs, but not from lice.
After an infestation
After an infestation, wash all clothes, bed linen, sleeping bags, towels, and so on, in water of at least 130 degrees Fahrenheit, then dry on hot cycle for at least 20 minutes.
Put items that cannot be washed into a plastic bag for 2 weeks, or have them dry-cleaned.
It is not necessary to fumigate the house, but soft furnishings can be treated with a spray and vacuumed.