BMJ Group Medical Reference
This information is for people who have a child with head lice. It tells you about permethrin, a treatment used for head lice. It is based on the best and most up-to-date research.
Does it work?
It may do. Some research has found that permethrin can get rid of head lice. One study suggests you may have to apply permethrin twice, within seven days, for it to work well.
But the only permethrin product suitable for head lice in the UK is a crème rinse. Doctors think it may be too diluted and is not left on the head long enough to work.
What is it?
Permethrin is a chemical that kills insects (an insecticide). It is a man-made (synthetic) version of natural insecticides called pyrethrins.
Permethrin is also used to get rid of many other types of insects on animals and crops, as well as to control scabies (a disease caused by mites that live on the skin) and pests in buildings.
You can buy permethrin from a pharmacy without a prescription as Lyclear Crème Rinse. This is a one percent rinse, which means one part of the chemical (permethrin) is used in 99 parts of solution (the liquid in which the chemical is dissolved). You rinse it out of your hair after 10 minutes. It's not suitable for babies younger than six months.
But doctors don't recommend Lyclear Crème Rinse to get rid of head lice. This is because it may be too diluted and is not left on the head long enough to work well.  Doctors recommend that lotions and liquids stay on your hair overnight to give them more chance of getting rid of all of your head lice. How to use permethrin
If you wish to try it, here's how to use permethrin as a crème rinse.
Check everyone in the household for live head lice before using this treatment. You should treat everyone with head lice at the same time.
Before you apply any treatment, remove clothes from the waist up.
Shampoo and towel-dry your hair.
Apply the crème rinse to the scalp and all the hair, and leave on for 10 minutes.
Rinse hair with water only. Do not shampoo the hair for at least 24 hours.
Check the hair for head lice after about eight hours to 12 hours with a louse detection comb. If the permethrin has worked, you should not find any live head lice.
Keep checking your own or your child's hair every two or three days for any newly hatched head lice. If you find head lice, repeat the treatment after seven days.
After about two weeks, check the hair of everyone who has been treated to make sure all the nits and head lice are gone.