BMJ Group Medical Reference
This information is for people who have a child with head lice. It tells you about malathion, a treatment used for head lice. It is based on the best and most up-to-date research.
Does it work?
Yes, malathion is likely to work against head lice. It may work better than some treatments because it kills the head lice eggs too. But malathion might not work if head lice have become resistant to it in the area where you live.
What is it?
Malathion is a chemical that kills insects (an insecticide). It is one of a group of compounds called organophosphates. There are many different organophosphates, and many are used to control pests on animals and crops. Some organophosphates are more poisonous than others, and malathion is one of the weaker chemicals in this group.
Some people are concerned that chemicals such as malathion can cause serious damage to their health and cause problems such as dizziness and numbness. The government committee that checks the safety of chemicals says there's no evidence that the low doses of malathion used in head lice treatments are harmful.  Because these treatments are not used very often or for very long the committee says the use of treatments does not need to be restricted.
Malathion rapidly kills both the head lice and their eggs. It should get rid of all the head lice after just one treatment, but your doctor or pharmacist will probably suggest you apply the treatment again after one week to be certain it has killed all the head lice.
Malathion comes as a liquid, a lotion, and a cream shampoo. You can buy malathion in a pharmacy or your doctor can prescribe it for you. The brand names include Derbac-M and Prioderm. It's not suitable for babies younger than six months.
Malathion lotion contains other substances that give it a strong smell. It has to be left on for several hours, so it is a bit inconvenient to use. It may be worth trying if other treatments haven't worked.How to use malathion
Check everyone in the household for live head lice before using this treatment. You'll want to treat everyone who has head lice at the same time.
Sprinkle malathion onto dry hair and work into the scalp and hair until they feel thoroughly moistened. Unless you have very short hair, you will need at least 50 millilitres (50 mL) to do this.
Wash your hands as soon as you've finished rubbing in the treatment.
Let your hair dry naturally. Do not use a hairdryer, and make sure you leave your hair uncovered.
Leave the treatment in your hair for 12 hours. Usually the most convenient way to do this is to leave it on overnight.
After 12 hours, wash your hair and rinse it thoroughly.
After rinsing your hair, and while it's still wet, go through it with a louse detection comb to remove the dead head lice and nits from your hair.
You should repeat this treatment after one week to be certain your hair is clear of head lice.
Do not use this treatment more than recommended by your doctor. Your doctor will probably suggest you try a different treatment if it doesn't work the first time you use it. The head lice may be resistant to malathion, which means this insecticide won't kill them.
If you get some of the treatment in your eyes, wash it out immediately with plenty of water.