Permethrin 1% creme rinse, sold in the US as Nix and other brands, is one of the most widely used over-the-counter treatments for head lice. Used correctly, alongside careful combing, it clears many cases. Here’s how to get the best result, and what to do if lice keep coming back.
How it works
Permethrin is an insecticide that attacks the nervous system of lice. It kills live lice and some eggs (nits), and leaves a small amount on the hair that can keep working for several days.
Who can use it
- Adults and children aged 2 months and over, following the label
- Babies under 2 months, and anyone pregnant or breastfeeding: ask a doctor first
- Don’t use it if you’re allergic to chrysanthemums or ragweed, or if the scalp is broken or infected
How to use permethrin 1%, step by step
- Wash the hair with a shampoo that has no conditioner, then towel dry. Conditioner can coat the hair and stop the treatment working.
- Shake the bottle and apply enough to soak the hair and scalp, especially behind the ears and at the back of the neck.
- Leave it on for 10 minutes, then rinse with warm water over a sink, not in the shower, to limit skin contact.
- Comb through with a fine-toothed nit comb, section by section, to remove dead lice and eggs.
- Don’t wash the hair again for 1 to 2 days.
- Check again and repeat on day 9 if you find live lice, to kill any lice that have hatched since.
Why it sometimes fails
In many parts of the US, head lice have become resistant to permethrin. If you still find live, moving lice 8 to 12 hours after treatment, or after the second treatment, the lice may be resistant. Repeating permethrin again and again won’t help.
Alternatives if permethrin doesn’t work
- Ivermectin 0.5% lotion (Sklice), available over the counter in the US since 2020. A single 10-minute treatment usually works without combing. See our guide to head lice treatment.
- Spinosad or malathion lotion, which need a prescription
- Wet combing alone with conditioner and a nit comb every 3 to 4 days for 2 weeks, which needs no chemicals
Around the home
- Wash pillowcases, hats and towels used in the last 2 days in hot water, or seal them in a bag for 2 weeks
- Soak combs and brushes in hot water for 10 minutes
- Check everyone in the home, and only treat people who have live lice
- There’s no need for insecticide sprays on furniture or carpets
Side effects
Mild itching, redness or tingling of the scalp is common and usually fades. Itching can also continue for a while after lice are gone, as a reaction to the bites. Wash off and get help if you notice swelling, a rash or trouble breathing.
Frequently asked questions
Is permethrin 1% the same as permethrin 5%?
No. The 1% creme rinse is for head lice and is sold over the counter. The 5% cream is a prescription treatment for scabies, which is applied to the whole body. See scabies symptoms and treatment.
Can my child go to school after treatment?
Yes. US health organisations advise that children don’t need to miss school because of head lice.
Do I need to treat the whole family?
Check everyone, but only treat people who have live lice.
More in our Lice and Parasites guide: all our articles on this topic in one place.
This article is for general information only and isn’t a substitute for advice from a doctor or pharmacist. Always read and follow the label.
