Malathion (Topical)

Prescribed as a pediculicide, Malathion is used to treat head lice infestations and can be applied as a topical solution.


Known as an insecticide or pediculicide, Malathion treats head lice infestations by killing the lice and their eggs. When applied, Malathion inhibits the acetylcholinesterase activity of eukaryote cells and inhibits cholinesterase. Once this has occurred, muscle spasms affect the existing lice and, ultimately, Malathion causes their death.

As well as being used to treat head lice, Malathion can be used as a remedy for lice infestations on other parts of the body. Although the medication has a relatively low toxicity to humans when it is used as a topical solution, caution must be shown when the medicine is applied. As children are often affected by head lice infestations, it is particularly important that they are monitoring during and following the use of Malathion.

Whilst Malathion is an effective treatment for lice infestations, some studies has shown that lice are becoming resistant to some topical treatments, such as Malathion. Due to this, patients should continue to check their scalp and other affected areas for some time after the treatment has been completed. In the majority of cases, however, Malathion is successful in treating the lice infestation.

Conditions Treated

Type Of Medicine

  • Pediculicide
  • Insecticide

Side Effects

When using Malathion or following treatment, patients may experience the following side-effects:

  • Itching, dry or burning eyes
  • Excessive tearing or discharge from the eyes
  • Swelling, pain or redness of the eyelid, eye and/or inner lining of the eyelid
  • Irritation or stinging of the scalp

If the symptoms are not severe and are not troublesome to the patient, further medical treatment may not be needed. However, in side-effects persist or are distressing for the patient, medical advice should be sought.

In addition to this, patients will need to inform a healthcare practitioner straight away if they develop the following side-effects when using Malathion:

  • Peeling and blistering of the skin
  • Swelling
  • Rash on the skin
  • Pain
  • Reddened skin

If patients experience any other adverse effects when using Malathion, they should also obtain medical advice.

When using Malathion, it is important that patient's follow their doctor's instructions and only use the appropriate of medication. If too much is used or if the medication is accidentally ingested, it can cause symptoms of an overdose. Patients should obtain emergency medical help if Malathion is ingested or if patients display any of the following symptoms:

  • Stomach or abdominal cramps
  • Restlessness or anxiety
  • Dizziness
  • Unsteadiness or clumsiness
  • Drowsiness
  • Mental depression or confusion
  • Trembling
  • Convulsions (seizures)
  • Pinpoint pupils
  • Diarrhea
  • Unusual weakness
  • Labored or difficult breathing
  • Increased sweating
  • Slow heartbeat
  • Increased watering of the eyes or mouth
  • Muscle twitching of the face, neck or of the eyelids
  • Loss of bladder or bowel control

If patients accidentally swallow or ingest Malathion, they should seek medical help straight away and should not wait for the symptoms of an overdose to occur. Patients will need to get to their nearest Emergency Room, call 911 and/or contact a Poison Control Center if Malathion has been swallowed.


If patients over the age of six years are prescribed Malathion for the treatment of head lice, it should be applied to the scalp and hair just once. In some cases, physicians may advise the patient to use the medication again, seven to nine days after the first application.

Generally, Malathion should be applied to dry hair and rubbed in until the scalp and hair are fully moistened by the medication. Following this, patients should wash and rinse their hands thoroughly to remove the solution from them. Patients should then let their hair dry naturally. It is not safe to cover the hair and/or use a hairdryer or other heating appliances whilst the solution is on the hair or scalp.

Malathion is a highly flammable substance so patients must show caution whilst it is on the hair and scalp. Electric heating appliances should not be used, patients should not smoke and should not go near any open flames after the solution has been applied.

Usually, Malathion should be left on the hair and scalp for approximately eight to twelve hours, before being washed with a standard shampoo and rinsed with clean water. Patients will then need to have their hair and scalp examined, and any remaining lice or eggs removed with a fine-toothed comb or nit comb. However, if patient's experience burning or skin irritation when Malathion is applied, they should wash the solution off straight away and should not leave it on for the full eight to twelve hours.

If Malathion is prescribed to pediatric patients, children should be monitored when the solution has been applied to ensure that they do not get the medication on other parts of their skin or in their mouth.

If lice or eggs are still present after seven to nine days, patients should seek medical advice and may be instructed to apply a second dose of Malathion.

Malathion should not be allowed to enter or get near to the eyes. If it does, patients should rinse their eyes with clean water and consult their physician straight away.

Patients should not use excessive amounts of Malathion and should not leave it on the affected areas for longer than advised. If too much solution is used or if it is left on for too long, it may be absorbed by the skin and patients could suffer very serious symptoms, such as an overdose. If this occurs, patients will need urgent medical treatment.

When using Malathion, patients should not use any other hair treatments, cosmetics or hair products.

If patients are unsure how to apply Malathion or how to use the solution, they should contact their physician or pharmacist for advice.

Potential Drug Interactions

Before patients apply Malathion to the scalp, hair or body, they should tell their physician if they are using any other medicines. This includes prescription medicines, over-the-counter medicines, vitamins and supplements.

As some medicines can interact with one another, patients may be unable to use Malathion if they are taking or using certain other remedies. In addition to this, patients will need to obtain medical advice before using any new medicines, supplements or vitamins, once they have applied Malathion solution.


In some instances, existing health problems or a history of certain conditions can affect the patient's use of Malathion solution. Due to this, patients should discuss their health with their physician before Malathion is prescribed to them. The following conditions may affect the suitability of Malathion as a treatment:

Although pediatric patients can be prescribed Malathion, specific studies into the effects of younger patients have only been carried out on patients over the age of six years. In some instances, doctors may prescribe Malathion solution to younger patients but it should not be used to treat patients under the age of one year.

Patients should contact their physician straight away if they experience a stinging sensation or burns when the solution is applied.

Similarly, patients should wash the medication off and seek medical help if they develop skin irritation once it has been applied.

Breathing in insecticides and pediculicides, such as Malathion, can be extremely harmful. This medication should be applied in a well-ventilated environment and patients should wash their hands straight after applying it. Patients may also wish to use a mask over their mouth and nose whilst the solution is on the hair and scalp as this can prevent them from breathing it in.

Patients should only use Malathion if they have been advised to do so by a physician.

As head lice are easy to transfer from one person to another, more than one individual in a household may be affected. Sharing items, such as, bedding, clothing, towels, scarves, hats, combs, hairbrushes and/or washcloths can lead to the spread of head lice.

If one person in a household has a head lice infestation, all members of the household should be checked and should seek medical advice if they require it.

Once Malathion solution has been applied, patients should wash items so that a re-infestation does not occur. For example, patients should wash bedding, clothes, linens, towels, hairpieces, combs, wigs, scarves, hats and washcloths in soapy, hot water or have them dry-cleaned, if it is appropriate to do so.

Similarly, the patient's room or home should be thoroughly cleaned and vacuumed to ensure that a re-infestation doesn't occur.

Although it may be acceptable to use Malathion during pregnancy, this medication may carry some risks to the patient and their unborn baby. Patients should seek medical advice and notify their physician before the use Malathion if they are pregnant.

It is not known if Malathion can be excreted in breast milk and whether it could cause harm to a nursing infant. Due to this, patients may be advised not to breastfeed whilst using this medication and should seek medical advice before doing so.

If patients have any known allergies, they should notify their doctor before Malathion is prescribed. This includes allergies to medicines, cleaning products, chemicals, animals, preservatives, dyes or any other substances. In rare cases, patients may develop an allergic reaction when using Malathion solution and, if so, they will require emergency medical treatment. An allergic reaction may be characterized by the following symptoms:

  • Hoarseness
  • Shortness of breath
  • Itching
  • Hives
  • Difficulty swallowing
  • Trouble breathing
  • Swelling, which may affect the nose, face, throat, lips, mouth or hands
  • Rash on the skin


If patients are required to keep Malathion at home, they must ensure that it is stored in a safe location and that children or pets cannot gain access to it. When storing Malathion, patients should following the manufacturer's instructions and the medication guidelines.

In most cases, Malathion can be stored at room temperature but it should always be kept in a closed container. Malathion will also need to be protected from heat, moisture and light, and should not be kept in an environment in which extreme temperatures may occur. As Malathion is highly flammable, it is important that it is not stored near an open flame or heat.

When disposing of Malathion, patients should ensure that they throw the medication away safely. Malathion should not be thrown out with regular household waste in case it causes harm to another person and old medicine should not be kept in the home. Instead, patients should contact their physician's office or pharmacist and use a designated medicine disposal service.


Although a head lice infestation can be an irritating and upsetting condition, it can usually be treated quickly and does not often cause any additional complications. However, it's important that patient's seek guidance from a physician before using Malathion and that they follow their doctor's advice when applying Malathion.

As Malathion is a strong insecticide, it can cause serious harm if it is used incorrectly or if it is swallowed. Providing Malathion is used appropriately, it should successfully kill the lice and eggs which are present in the patient's hair or on their scalp. Once this has been achieved and any remaining lice or eggs have been removed, patients should not require any further treatment.