Malathion liquid (Derbac-M)

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Use two applications of malathion liquid, seven days apart.

Leave each application on for 12 hours if treating lice, or 24 hours if treating scabies; then wash it off with soap and water.

Affected family/contacts should all be treated on the same day.

Type of medicineAn insecticide
Used forTreatment of scabies, head lice and crab lice
Also calledDerbac-M®
Available asLiquid for use on the skin and scalp

Malathion liquid contains an insecticide. It kills insects (parasites) that live on humans, such as head lice, the scabies mite and crab lice. Two applications of treatment with malathion liquid are needed, one week apart.

Head lice are common in children but can affect anyone of any age. Close hair-to-hair contact is usually needed to pass lice on. Head lice cannot jump or fly but walk from one head to another. They are tiny grey/brown insects, about the size of a sesame seed. Head lice cling to hairs but stay close to the scalp which they feed off. Many people with head lice do not have any symptoms, although some may have an itchy scalp.

Scabies is an itchy skin disorder that leads to a rash. It is caused by an infestation with a parasite - the scabies mite. The mite lives on the skin and burrows into it. Scabies is contagious and spreads to others through close skin-to-skin contact. The hand is the most common site to be first affected, probably from prolonged hand-holding with an infected person. Close skin-to-skin contact when having sex is another common way of catching scabies.

Crab (pubic) lice are tiny insects that live on humans, usually in the pubic hair. They are passed on through close body contact, such as when having sex. Infestation with crab lice can cause itching but not everyone affected has symptoms. Crab lice are grey or brown in colour. They get their name because some of their legs have crab-like claws.

Malathion liquid is available on prescription, or you can buy it without a prescription at a pharmacy. It is easy to apply and normally works well if used properly.

To make sure this is the right treatment for you (or your child), before you start using malathion liquid it is important that your doctor or pharmacist knows:

  • If any areas of skin are sore or infected.
  • If you are pregnant or breast-feeding.
  • If it is for a child under 6 months old. This is because, in very young children, it should only be used on the advice of a doctor.
  • If you have ever had an allergic reaction to a medicine or skin product.
  • Before you (or your child) start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about applying malathion liquid and will provide you with a full list of the side-effects which you could experience from using it. Two applications of treatment are needed, one week apart.
  • To treat head lice: apply the liquid to dry hair and rub it into the scalp. Let the hair dry again naturally. Leave it on for 8-12 hours (preferably overnight) and then shampoo it out. Comb through the hair, using a 'nit comb', while it is still wet to remove the dead lice and eggs (nits). You will need to use malathion a second time, seven days after the first treatment. Apply the liquid in the same way as the first time. Using two treatments helps to ensure that any lice emerging from eggs having survived the first treatment are killed.
  • To treat scabies: apply the liquid over your whole body including your face, neck, scalp and ears, but try to take care not to get any into your eyes. Remember to include awkward places such as your back, the soles of your feet, between your fingers and toes, under your fingernails, and your genitals. Malathion should be applied when your skin is cool and dry, so if you have just had a bath or shower, wait for a little while to let your skin cool before you apply it. Pay special attention to the areas where mite burrows can commonly occur - the front of your wrists and elbows, beneath your breasts, your armpits, and around the nipples in women. Let your skin dry naturally after applying the treatment and leave it on for 24 hours. Each time you wash your hands using soap during this 24 hours, reapply the liquid to your hands afterwards. After 24 hours, remove the treatment from your skin by having a bath or a shower. You will need to use malathion a second time, seven days after the first treatment. Apply the liquid in the same way as the first time.
  • To treat crab (pubic) lice: apply the liquid over your whole body including your face, neck, scalp and ears, but try to take care not to get any into your eyes. Remember to include awkward places and pay particular attention to all hairy areas (such as eyebrows and facial hair) and your genitals. Let your skin dry naturally. Leave the treatment on for 12 hours (or overnight) and then wash it off by having a bath or a shower. You will need to use the liquid a second time, seven days after the first treatment. Apply it in the same way as the first time. Using two treatments, a week apart like this, helps to ensure that all the lice are killed.
  • If you are using malathion for head lice, all family members who are affected should be treated at the same time. It can also help to comb the hair with a nit comb every four days. Comb through small sections of wet hair and remove any lice you find. It can take half an hour or so to do this over the whole scalp. Continue to do this twice a week until your hair is free from lice on three consecutive sessions.
  • If you have scabies, all your household members, close contacts and sleeping/sexual partners should also be treated - even if they have no symptoms. This is because it can take up to six weeks to develop symptoms after you become infected. Close family and partners may be infected but have no symptoms, and may pass on the mite. Everyone who is treated, should be treated on the same day.
  • If you have crab lice, your recent close contacts and sexual partners should also be treated if they are infected. It is important to remember that lice may be present even without other symptoms such as itching. If you have caught crab lice from a sexual partner, you should also be tested for other sexually transmitted infections.
  • Do not use malathion more frequently or for more times than is recommended. If you feel the treatment has not been successful, make an appointment to see your doctor for further advice. An alternative preparation may be recommended for you.

If you have scabies, the following also applies:

  • If you are applying malathion liquid to an infant or young child, put mittens on your child to stop them licking the treatment off their hands. Don't apply the liquid to areas around their mouth where it could be licked off.
  • Children should stay off school until the first application of treatment for scabies has been completed.
  • Clothes, towels and bed linen should be machine-washed at 50°C or above after the first application of treatment. This kills the scabies mites. Keep any items of clothing that cannot be washed, in plastic bags for at least 72 hours to contain the mites until they die. Alternative options to kill any mites on clothes and linen are ironing the item with a hot iron, dry cleaning or putting items in a dryer on the hot cycle for 10-30 minutes. It is not necessary to fumigate living areas or furniture or to treat pets.
  • You will still be itchy for a while after successful treatment. If the itching becomes troublesome to you, your doctor or pharmacist will be able to advise you regarding suitable products to ease this. Moisturising creams can provide temporary relief from itching.
  • It is normal for it to take up to 2-3 weeks (and sometimes up to six weeks) for the itch to go completely after scabies mites have been killed. You should, however, see a doctor if the itch persists longer than 2-3 weeks after treatment. This is because sometimes the first insecticide does not work and you may need to use a different one.
  • Some people may develop a secondary skin infection which may need antibiotic treatment. If you suspect this is the case for you, you should make an appointment to see your doctor.

Malathion can occasionally cause skin irritation. This should soon pass but, if it is severe or becomes troublesome (or if you experience any other symptoms which you think may be due to the treatment), please ask your doctor or pharmacist for further advice.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

Make sure that the person supplying this medicine knows about any other medicines that you are taking or using. This includes any prescribed medicines, and any medicines you buy such as herbal and homeopathic medicines.

This preparation is for use on the skin only. If someone swallows some of it by accident, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

If you are having an operation or any dental treatment, tell the person carrying out the treatment which medicines you are taking or using.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine, please ask your pharmacist.

Further reading & references

  • Manufacturer's PIL, Derbac M® Liquid; Forum Health Products Limited, The electronic Medicines Compendium. Dated December 2011.
  • British National Formulary; 69th Edition (Mar 2015) British Medical Association and Royal Pharmaceutical Society of Great Britain, London

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Dr Hannah Gronow
Document ID:
3328 (v26)
Last Checked:
Next Review:
The Information Standard - certified member

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