Pubic lice (crabs): how to recognise, treat and get checked

Pubic lice, also called crabs, are greyish-brown insects of about three millimetres that cling to coarse body hair. They cause stubborn itching in the pubic area, usually a few weeks after transmission. Around 2 percent of adults deal with them at some point.

Unpleasant, but not dangerous. A cream from the pharmacy is usually enough.

Here is what almost no page mentions, and what we think matters most about this topic: pubic lice rarely arrive alone. In a study among visitors to an STI clinic, 31.4 percent of people with pubic lice had another STI at the same time (Chapel et al., 1979).

That second infection often causes no symptoms at all. Unlike the lice, it is measurable.

What exactly are pubic lice?

A pubic louse is a parasite that feeds on small amounts of blood from your skin. The medical name is pediculosis pubis, after the insect Pthirus pubis. It holds onto coarse hair, so mainly pubic hair, but also armpits, chest hair, beards, eyebrows and sometimes eyelashes. It cannot survive on scalp hair, which is too fine.

The louse is flat and wide, which is where the nickname crabs comes from.

Adult lice live about three to four weeks on the skin. Away from a body they last only a day or two. Their eggs, called nits, stick to the hair shaft as small yellowish-white dots and hatch after roughly a week.

The itch does not come from the insect itself but from an allergic reaction to its saliva. That is why a first infestation can take two to four weeks before you notice anything.

How common are pubic lice?

Estimates range from 0.3 to 4.6 percent per year, with a prevalence of around 2 percent among adults. That makes crabs rarer than chlamydia, but hardly unusual. In a group of fifty people the odds are real that someone has had them.

The numbers have also been falling for years.

Researchers attribute this mainly to pubic hair removal: less coarse hair simply means less habitat for the louse (Patel et al., 2021). It is one of the few infections where a fashion trend appears to change the course of the disease at population level.

What strikes us about that: because it is getting rarer, people recognise it less quickly. They think of a yeast infection or shaving irritation first, and spend weeks treating the wrong cause.

How do you recognise pubic lice?

You recognise pubic lice by three things together: persistent itching in the pubic hair that is worse at night, yellowish-white dots stuck to the hairs that cannot be wiped off, and sometimes reddish-brown specks in your underwear. That last one is louse droppings.

The insects themselves are visible, but you have to look carefully. They move slowly and are roughly the colour of your skin.

One detail often puts people on the trail: bluish-grey marks on the skin of the abdomen or inner thighs. These are called maculae ceruleae and are tiny bleeds at the bite sites.

Scratching muddies the picture. The skin gets irritated, crusts form, and suddenly it looks like eczema or a fungal infection. In our article on pubic lice symptoms we go through what each complaint actually looks like.

Pubic lice, scabies or something else?

Itching in the pubic area has many possible causes, and they are hard to tell apart by eye. The difference usually lies in the timeline, in what you can see, and in the location. The table below places the five most common ones side by side.

That last row is the reason this article exists. The four conditions you can see are not found by a laboratory. The infection you cannot see is.

If your itch does not fit this list, our overview of genital itching causes goes further.

Does an STI test find pubic lice?

No. A laboratory STI test works on blood, urine or a swab and looks for bacterial DNA or for antibodies. A pubic louse is an insect on your skin. There is no blood value that shows it, and the same is true for scabies. Both are identified by looking.

That sounds like a gap, but it is not quite the whole story.

Pubic lice almost always pass through intimate physical contact. That is exactly the contact through which chlamydia, gonorrhoea, trichomonas, syphilis or HIV can pass. The lice are visible and itch, so you notice them. The rest often runs without symptoms.

Hence the 31.4 percent from the introduction. In that clinic series, nearly one in three people with pubic lice had something else alongside it (Chapel et al., 1979). The RIVM guideline for scabies states the same principle for mites: consider STI testing if the infestation was probably acquired through sexual contact.

Say you had a new partner, developed itching three weeks later, and found crabs. You know about the lice within a day. About a possible chlamydia you know nothing until you have it checked. A combined test for chlamydia, gonorrhoea and trichomonas covers the three that are most common in the Netherlands.

What you do with that result is a conversation with your GP. We provide the measurement, not the diagnosis.

Two people, the same crabs, a different outcome

Take two people who find crabs in the same week. Both with 3 millimetre insects in the pubic hair, both with itching that started about three weeks earlier. Up to here their story is identical.

The first treats with permethrin, repeats after a week, and is done. Finished, and rightly so.

The second does exactly the same, and also gets checked for chlamydia, gonorrhoea and trichomonas. That result comes back with chlamydia, without there ever having been a symptom. Without the lice he would have had no reason to look at all.

The difference between those two is not how bad their infestation was. It is whether the visible part became a reason to look at the invisible part.

For roughly one in three people that second track leads somewhere (Chapel et al., 1979). For the other two it does not. That is also an outcome, and for many people it is the reason they had it done.

How do you treat pubic lice?

You treat pubic lice with a product that kills both the lice and the nits. Permethrin cream is the usual first choice in the Netherlands and is available without a prescription. According to Thuisarts.nl you apply it and rinse it off after 8 to 12 hours. After a week you repeat the treatment.

That second round is where things most often go wrong.

Nits that had not yet hatched during the first treatment hatch afterwards. Skip the repeat and it simply starts again. This is usually not resistance but what the literature calls pseudoresistance: the product works, the application did not (Patel et al., 2021).

If permethrin genuinely fails, second-line options such as phenothrin, malathion or ivermectin exist. Those are a conversation with your GP or pharmacist. The Cochrane review on scabies found no difference in effect between permethrin and ivermectin after two weeks (Rosumeck et al., 2018).

More on the practical side, including what a nit comb does and does not achieve, is in our article on pubic lice treatment.

How do you get pubic lice?

Pubic lice pass almost exclusively through direct, prolonged physical contact where pubic hair meets pubic hair. Sex is the most common route. A louse cannot jump and cannot fly, so it has to walk across.

Bedding, towels and clothing can play a part, but far less often than people assume. Away from a body a louse lasts about one to two days.

A toilet seat is practically no risk. The louse needs hair to grip, and smooth plastic offers it nothing.

Interestingly, pubic lice have become less common worldwide than a few decades ago. Researchers point to pubic hair removal: less coarse hair means less habitat (Patel et al., 2021). Whether shaving helps once you already have them is a different question, answered in how you get pubic lice.

What about clothing, bedding and partners?

Wash clothing, towels and bedding used in the last two days at 60 degrees or hotter. That is warm enough to kill lice and nits. Anything that cannot go in the wash goes into a sealed bag in the freezer for a day. Thuisarts.nl describes the same approach.

Large cleaning operations are unnecessary. The louse lives on people, not on your sofa.

The harder part is the conversation you would rather avoid. Partners from the past two months can be infested without noticing, and without treatment it travels back and forth. How to approach that conversation is covered in notifying your partner.

There is little here to be ashamed of. Crabs say nothing about hygiene and nothing about how many partners you have had.

When is your GP the better option?

See your GP if the itching persists after two full treatments, if the skin becomes inflamed or weepy, if there are lice in your eyelashes, or if you are unsure it is pubic lice at all. Permethrin is not advised close to the eyes, so eyelashes call for a different approach.

If you cannot tell pubic lice from scabies, that alone is a good reason to have someone look. Scabies needs different treatment and household members treated alongside you.

Children with lice in their eyelashes deserve extra attention, because the route of transmission should always be asked about there.

And if the itch is gone but something still nags about that one contact, the question is no longer about lice. It is about what you cannot see.

What we make of it

Pubic lice are one of the few STI-adjacent conditions where you can more or less make your own diagnosis. Either you see the insect or you do not. Treatment costs a cream and two rounds of patience.

Which is exactly why we find it a shame that most pages about crabs stop there. The lice are the visible part of a moment of contact. The rest of that moment is not visible.

If you choose to look further, do it at the right time: chlamydia and gonorrhoea can generally be shown reliably from around two weeks after the risk. Discuss your results with your GP afterwards, certainly if symptoms persist.

References

• Chapel TA, Katta T, Kuszmar T, DeGiusti D. Pediculosis pubis in a clinic for treatment of sexually transmitted diseases. Sexually Transmitted Diseases, 1979. PMID 531724
• Patel PU, Tan A, Levell NJ. A clinical review and history of pubic lice. Clinical and Experimental Dermatology, 2021. PMID 33811771
• Rosumeck S, Nast A, Dressler C. Ivermectin and permethrin for treating scabies. Cochrane Database of Systematic Reviews, 2018. PMID 29608022
• RIVM, LCI guideline scabies. lci.rivm.nl
• Thuisarts.nl, Ik heb schaamluis. thuisarts.nl

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.