Approved indications: Topical malathion 0.5% lotion is approved to treat infestations of head lice and their eggs on the scalp hair. It is generally used in adults and children 6 years of age and older, with safety and effectiveness not established in children younger than 6 years and the product contraindicated in neonates and infants.

Off‑label uses: In some settings outside the U.S., malathion has been used off‑label for difficult cases of pubic lice or scabies, but these uses rely on limited evidence and carry more concern for irritation and systemic absorption, so other agents (such as permethrin, ivermectin, or other approved scabicides/pediculicides) are usually preferred.

Efficacy expectations: Malathion is both pediculicidal and partially ovicidal, so live lice usually die within the first day after treatment and many eggs are also killed; clinical trials show that the large majority of patients are free of live lice within about a week after a single properly applied treatment, with a second treatment 7–9 days later used only if live lice remain.

Comparison with similar drugs: Compared with over‑the‑counter permethrin or pyrethrin products, malathion can be more effective against lice that have become resistant, and its partial activity against eggs may reduce the need for retreatment, but its strong alcohol base, flammability, odor, and risk of skin irritation or burns mean it is often reserved for cases that fail or cannot use first‑line treatments.

Typical dosing (head lice): Adults and children 6 years and older apply enough 0.5% malathion lotion to dry hair and scalp to thoroughly wet the hair and skin, including the back of the head and neck, then allow hair to dry naturally and leave the medication in place for 8–12 hours before washing it out with shampoo and rinsing over a sink or tub with warm (not hot) water.

How to apply: Do not use conditioner before applying, and do not cover the hair with a shower cap or towel while it is wet with the product; keep the medicine out of the eyes, mouth, nose, and vagina, and do not use it on eyebrows or eyelashes. After rinsing, a fine‑tooth nit comb may be used to remove dead lice and nits, and clothing, bedding, and personal items should be cleaned according to lice‑control recommendations to prevent reinfestation.

Retreatment and duration: A second application is recommended only if live (crawling) lice are still seen 7–9 days after the first treatment; the medicine should not be used more frequently or for longer than directed because of the risk of irritation and systemic absorption.

Special instructions and precautions: Because the lotion contains a high percentage of alcohol, avoid smoking, open flames, and heat‑producing hair appliances while applying it and until the hair is completely dry; use in a well‑ventilated area and supervise children closely during application and rinsing.

Missed dose / forgotten retreatment: If a planned second treatment is missed, apply it as soon as you remember, as long as it is still within the recommended window and live lice are present, then resume normal activities; do not apply multiple back‑to‑back treatments or extra amounts to “catch up.”

Overdose: If too much product is used, applied to broken skin, or accidentally swallowed, rinse exposed skin thoroughly with water, remove contaminated clothing, and seek immediate help from a poison control center or emergency medical services, especially if symptoms such as trouble breathing, severe nausea, muscle twitching, or confusion occur.

Common side effects: The most frequent effects are mild and temporary, including stinging or burning of the scalp, redness or irritation of the skin, dryness or increased dandruff, and an unpleasant odor; these usually start soon after application and improve after the lotion is washed out.

Serious or rare adverse effects: Rarely, chemical burns (including second‑degree burns) of the scalp or skin have been reported; accidental eye exposure can cause painful redness and irritation; if too much is absorbed or swallowed, signs of organophosphate poisoning (such as excessive sweating or salivation, nausea, vomiting, diarrhea, muscle twitching or weakness, trouble breathing, confusion, or seizures) can occur and require emergency care.

Warnings and precautions: Malathion lotion is for external use on scalp hair only and must not be used on neonates or young infants; safety in children under 6 years has not been established, and many clinicians avoid it in small children or those with asthma or very irritated skin because of fume and absorption concerns. During treatment, avoid open flames, smoking, or heated hair appliances because the product is highly flammable. Use caution in pregnancy and breastfeeding (animal data are reassuring but human data are limited), applying only if clearly needed and avoiding infant contact with treated, wet hair; people with conditions that increase sensitivity to cholinesterase inhibitors (such as myasthenia gravis, certain neurologic diseases, or recent exposure to other organophosphate insecticides) should discuss risks carefully with a clinician.

Relative safety versus other options: When used correctly on intact scalp skin, systemic side effects are uncommon and malathion is generally safe, but compared with some newer agents it carries more risk of skin irritation, strong odor, and flammability, so it is often chosen when other treatments are unsuitable or have failed.

Reporting and staying informed: Patients and caregivers should report bothersome or unexpected side effects to their healthcare provider and can report directly to the FDA’s MedWatch adverse‑event reporting program; updated safety information is available through the FDA and the product’s prescribing information or patient medication guide.

Drug and product interactions: Because malathion lotion is used on the skin and systemic absorption is generally low, clinically important drug–drug interactions are uncommon; however, combining it with other organophosphate or carbamate insecticides or with medications that also inhibit cholinesterase (for example, some drugs for Alzheimer’s disease or myasthenia gravis) could theoretically increase the risk of toxicity if significant absorption occurs.

Other products, foods, and alcohol: Usual foods and drinks do not interact with this topical medicine, but alcohol, heat, or flames applied externally are a concern because the lotion is highly flammable; avoid hair sprays, alcohol‑based styling products, or heated styling tools until the hair is completely dry and the product is washed out.

Medical conditions requiring caution: Use with extra care, and only under medical supervision, in people with asthma or other significant lung disease (fumes may irritate), seizure disorders, myasthenia gravis or other neuromuscular diseases, serious heart disease, active skin infections or open sores on the scalp, or in those who have recently been exposed to other organophosphate pesticides.

Age‑related precautions: Malathion lotion should not be used in neonates or young infants and has not been adequately studied in children under 6 years; older adults can generally use it, but fragile skin or multiple comorbidities may increase the risk of irritation or systemic effects.

Monitoring: No routine blood tests or special monitoring are needed for most patients; caregivers should watch for signs of skin burns, allergy (such as widespread rash, swelling, or trouble breathing), or cholinergic symptoms (such as excessive sweating, salivation, nausea, or muscle weakness) and seek immediate medical attention if these occur.

Q: How long should I leave malathion lotion on my hair?
A: It is usually left on dry hair and scalp for 8–12 hours, or exactly as directed on your prescription label, then washed out with shampoo and warm water.

Q: Can I use a hair dryer or smoke while malathion is on my hair?
A: No; the lotion contains a high amount of alcohol and is very flammable, so you must avoid smoking, open flames, and heated hair appliances until your hair is completely dry and the product has been washed out.

Q: Is malathion safe to use in pregnancy or while breastfeeding?
A: Animal studies have not shown birth defects and the product is classified as pregnancy category B, but human data are limited, so it should be used in pregnancy or during breastfeeding only if clearly needed and after discussing options with a healthcare provider.

Q: Can I use malathion on my child who is younger than 6 years old?
A: Safety and effectiveness have not been established in children under 6 years, and the lotion should not be used in neonates or young infants, so other head‑lice treatments are preferred for younger children unless a specialist advises otherwise.

Q: What should I do if live lice are still present after treatment?
A: If live lice are seen 7–9 days after the first treatment, a second application is usually recommended; if lice persist after two properly applied treatments, contact your healthcare provider to check for resistance, reinfestation, or the need for an alternative medicine.

Q: Do I still need to comb out nits after using malathion?
A: Malathion kills many, but not all, eggs, so using a fine‑tooth nit comb after treatment can help remove dead lice and remaining nits, improve cosmetic appearance, and reduce the chance of confusion between old and new infestation.

Storage: Store malathion lotion at room temperature (about 68–77°F / 20–25°C), tightly closed, away from heat, sparks, open flames, and direct sunlight because it contains a high percentage of flammable alcohol; keep out of reach of children and do not store in the bathroom where it may overheat.

Handling: Use in a well‑ventilated area, and do not smoke or use hair dryers, curling irons, or other electrical heat sources while the hair is wet with the product; allow hair to dry naturally and uncovered.

Disposal: For small leftover amounts, keep the cap on and place the bottle in household trash unless local rules require hazardous‑waste disposal; do not pour large quantities down the sink, toilet, or outdoors, and do not burn the container; for expired or unwanted product, ask a pharmacist or local waste authority about medicine take‑back or hazardous‑waste programs.