Treatment of Head Lice (Pediculosis Capitis)
First-Line Treatment: Permethrin 1%
Permethrin 1% cream rinse is the first-line treatment for head lice in all age groups except infants under 2 months, applied to damp towel-dried hair for exactly 10 minutes, then rinsed with warm water, with a mandatory second application 7-10 days later. 1, 2, 3
Application Technique
- Wash hair first with non-conditioning shampoo (conditioning products prevent proper adherence) and towel dry until damp—not soaking wet 2, 3
- Apply permethrin to the scalp, all hair shafts, hairline, neck, temples, and forehead (especially important in infants and elderly) 3
- Leave on for exactly 10 minutes—not longer or shorter 1, 3
- Rinse over a sink with warm water (not hot) to minimize systemic absorption 1, 3
- Second application on day 7-10 is mandatory because permethrin has only 70-80% ovicidal activity, meaning 20-30% of eggs survive the first treatment 1, 2, 3
Safety Profile
- Permethrin has extremely low mammalian toxicity and does not cause allergic reactions in patients with plant allergies 1, 2
- Safe for children over 2 months of age 1
Second-Line Treatment: Malathion 0.5%
Switch to malathion 0.5% lotion if live lice are confirmed 7-10 days after a second properly applied permethrin treatment—do not apply permethrin a third time, as this indicates resistance. 1
When to Use Malathion
- Documented resistance to permethrin 1
- Treatment failure despite correct permethrin application 1
- Malathion kills permethrin-resistant lice approximately 10 times faster than permethrin 1
Application Technique
- Apply to dry hair (not damp like permethrin) 1, 2
- Allow to air dry naturally—do not use hair dryers or heat sources 1, 2
- Leave on for 8-12 hours (can apply at bedtime and wash off in morning) 1, 2
- Has the highest ovicidal activity (~98%) of all treatments, so a single application is often sufficient 1, 2
- Reapply in 7-9 days only if live lice are still present 1
Critical Safety Warnings
- Contains 78% isopropyl alcohol—highly flammable 2
- Keep away from open flames, cigarettes, hair dryers, and heat sources 2
- Risk of severe respiratory depression if ingested 1
- FDA-approved for children ≥6 months, but contraindicated in children <24 months 1
Alternative First-Line Options
Spinosad 0.9% Topical Suspension
- Achieves high cure rates with a single 10-minute application 1
- Apply to dry hair and scalp, leave for 10 minutes, then rinse thoroughly 1
- Does not require a second application in most cases 1
Pyrethrins with Piperonyl Butoxide
- Apply to dry hair for 10 minutes, then rinse 2
- Requires second application in 7-10 days 2
- Neurotoxic to lice but extremely low mammalian toxicity 1
- Can be applied to dry hair, allowed to air dry, then washed off after 8-12 hours 1
Benzyl Alcohol 5%
- FDA-approved for children ≥6 months 1
- Kills lice by asphyxiation 1
- Requires repeat application in 7 days 1
- More than 75% of patients are lice-free 14 days after initial treatment 1
Special Populations
Infants <2 Months
- Permethrin is not recommended in this age group 1
- Manual removal with fine-toothed nit comb is safest option 1
Pregnant or Lactating Women
- Permethrin or pyrethrins with piperonyl butoxide are the safest options, though resistance may limit efficacy 1
- Avoid malathion due to high alcohol content and systemic absorption concerns 1
Permethrin-Allergic Patients
- Use malathion 0.5% as first-line alternative 1, 4
- Spinosad 0.9% or benzyl alcohol 5% are also appropriate 1
Treatments to Avoid
Lindane 1%
- Do not use as first-line treatment due to severe safety concerns 1, 2
- Risk of seizures, especially in children 2
- Low ovicidal activity (30-50% of eggs not killed) 1
- Widespread resistance 1
- Should only be used when all other treatments have failed 1
Oral Ivermectin
- Not FDA-approved for pediculosis 1
- Should not be used in children weighing <15 kg due to risk of blood-brain barrier penetration 1
- If used: single dose of 200 mcg/kg, repeated in 10 days 1
Critical Management Points
Who to Treat
- Only treat individuals with live lice or nits within 1 cm of the scalp 1, 2
- Examine all household members 1
- Treat family members who share a bed with the infected person 2
Environmental Decontamination
- Wash all clothing, bedding, and linens in hot water and dry on hot cycle on the same day as treatment 2, 3
- Wash hair care items (combs, brushes) in hot water 2, 3
- Remove items that cannot be washed from body contact for at least 72 hours (lice cannot survive off the human body for more than 2-3 days) 2, 3
- Fumigation of living areas is not necessary 3
Nit Removal (Optional but Helpful)
- Not necessary to prevent spread, but can decrease diagnostic confusion 2
- Apply vinegar or vinegar-based products to hair for 3 minutes before combing to help loosen nits 1, 2
- Use fine-toothed nit comb 2
Common Pitfalls and How to Avoid Them
Post-Treatment Itching is NOT Treatment Failure
- Itching or mild burning of scalp after treatment is common and persists for many days due to inflammatory response 1, 3
- Do not retreat based on itching alone—only retreat if live lice are seen 7-10 days after treatment 2, 3
- Topical corticosteroids and oral antihistamines may help relieve post-treatment inflammation 1, 3
Most "Resistance" is Actually Improper Application
- Before assuming resistance, consider: misdiagnosis, noncompliance, reinfestation from untreated contacts, or improper application technique 1, 2, 3
- Improper application is the most common cause of treatment failure, not resistance 1
- Reinfestation from untreated household contacts or contaminated fomites is more common than true treatment failure 1
Application Errors to Avoid
- Do not use conditioning shampoo before permethrin—it prevents proper adherence 3
- Do not apply permethrin to soaking wet hair—towel dry first 3
- Do not rinse with hot water—use warm water to minimize absorption 3
- Do not skip the second application for permethrin—it is mandatory 3
- Do not use heat sources with malathion due to flammability risk 2