Pubic lice treatment: what permethrin does and does not do

The standard pubic lice treatment is permethrin cream, available without a prescription. You apply it to the hair-bearing area, rinse it off after 8 to 12 hours, and repeat the whole treatment after roughly a week. That repeat is not extra insurance, it is a necessary part of the course.

Skip it and there is a good chance the infestation returns.

The reason is that products like permethrin kill adult lice well but do not kill every nit. Eggs that had not yet hatched go on to hatch afterwards.

How does permethrin work against pubic lice?

Permethrin is a synthetic version of pyrethrin, a compound from chrysanthemums. It paralyses the louse's nervous system, killing it within hours. According to Thuisarts.nl you leave the cream on for 8 to 12 hours, so in practice you apply it in the evening and rinse it off in the morning.

Treat the whole hair-bearing area, not only the spot that itches.

That means the pubic area, groin, natal cleft, and where relevant the abdomen, chest, armpits and legs. Lice walk away from wherever conditions turn unpleasant, so half-treated skin is an invitation.

The Dutch Farmacotherapeutisch Kompas lists permethrin as first choice for pediculosis. Patel and colleagues likewise place permethrin and pyrethrins in the first line, with phenothrin, malathion and ivermectin second (Patel et al., 2021).

Why do you have to repeat the treatment?

You repeat because nits are better protected than adult lice. Some eggs survive the first round and hatch over the following days. A second treatment after seven to ten days catches that new generation before it can lay eggs of its own.

Seven days is not an arbitrary number.

Nits hatch after roughly a week, and a young louse then needs another week or so to reproduce. The window between those two moments is exactly where the second round belongs.

Put day 7 in your phone. It is the one step people consistently forget.

Does Prioderm work against pubic lice?

Prioderm contains malathion and is mainly used against head lice in the Netherlands. Malathion appears in the literature as a second-line option for pubic lice, meaning when permethrin does not work (Patel et al., 2021). Whether it suits your situation depends on your skin, your age and any pregnancy.

That is a question for your pharmacist, not for a blog.

More important than the choice of product is usually the way it is used. Patel's review distinguishes true resistance from pseudoresistance: the product worked fine, but it was left on too briefly, applied too sparingly, or the second round was skipped.

Do nit combs or shaving work?

A fine nit comb removes loose nits and dead lice, but it is not a treatment on its own. Nits are firmly cemented on and some always stay put. Combing is useful alongside the cream, not instead of it.

Shaving is more nuanced than people assume.

Thuisarts.nl mentions shaving pubic hair as an alternative. Even so, it rarely resolves everything, because lice can also sit in armpit hair, leg hair or beard hair, which most people do not shave. What shaving does and does not achieve is covered in how you get pubic lice.

How do you stop it coming back?

Two things decide whether it returns: the second round, and whether partners are treated too. Thuisarts.nl advises informing sexual partners from the past two months. Without that, the infestation travels back and forth between people who were each treated at slightly different times.

Also wash clothing, towels and bedding from the last two days at 60 degrees or hotter.

Anything that cannot be washed goes into a sealed bag in the freezer for a day. Deep-cleaning the house is unnecessary, because the louse lives on people. How to open that conversation with a partner is covered in notifying your partner.

When should you see a GP?

See your GP if live lice remain after two full treatments, if the skin becomes inflamed or weepy, if there are lice in eyelashes or eyebrows, or if you are pregnant or breastfeeding. Permethrin is not suitable near the eyes.

If you doubt the diagnosis, a clinician's look is faster than another round of cream.

And because pubic lice often travel with a second infection that causes no symptoms (31.4 percent in one STI clinic series, Chapel et al., 1979), some people also choose to get checked for chlamydia, gonorrhoea and trichomonas. The full picture sits in our main article on pubic lice.

References

• 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
• 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
• 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.