Head Lice Treatment
First-Line Treatment: Permethrin 1%
Permethrin 1% cream rinse is the recommended first-line treatment for head lice, 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 1% to cover all hair and scalp thoroughly, paying particular attention to the back of head and neck 1, 2
- Leave on for exactly 10 minutes—not longer or shorter 2
- Rinse over a sink with warm water (not hot) to minimize systemic absorption 2
- 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
- Post-treatment itching is normal and persists for days due to inflammatory response—this is not treatment failure and should not prompt retreatment 1, 2, 3
Second-Line Treatment: Malathion 0.5%
If live lice are confirmed 7-10 days after a second properly applied permethrin treatment, switch to malathion 0.5% rather than applying permethrin a third time due to likely resistance. 1
When to Use Malathion
- Documented resistance to permethrin or pyrethrins 1
- First-line treatments fail despite correct application 1
- Malathion kills permethrin-resistant lice approximately 10 times faster than permethrin 1
Application Technique (Per FDA Label)
- Apply to DRY hair (not damp like permethrin) in amount sufficient to thoroughly wet hair and scalp 4
- Pay particular attention to back of head and neck 4
- Allow hair to dry naturally—use no electric heat source and leave hair uncovered 1, 4
- Leave on for 8-12 hours (can apply before bedtime) 1, 3, 4
- After 8-12 hours, shampoo and rinse, then use fine-toothed comb to remove dead lice and eggs 4
- Reapply in 7-9 days only if live lice are still present 1, 4
Critical Safety Warnings
- Malathion contains 78% isopropyl alcohol, making it highly flammable—avoid open flames, sparks, and electric heat sources during application and drying 3, 4
- Has the highest ovicidal activity (~98%) of all treatments, often requiring only a single application 1, 3
- Approved for children ≥6 months, contraindicated in children <24 months 1
- Risk of severe respiratory depression if ingested 1
Third-Line Treatment Options
Spinosad 0.9% Topical Suspension
- Achieves high cure rates with a single 10-minute application 1
- Apply to dry hair and scalp for 10 minutes, then rinse thoroughly with warm water 1
- Rinse over a sink to limit skin exposure 1
Benzyl Alcohol 5%
- Approved for children >6 months 1
- Kills lice by asphyxiation 1
- Requires repeat application in 7 days 1
- More than 75% of subjects lice-free 14 days after initial treatment 1
Topical Ivermectin 0.5% Lotion
- Requires only a single application 5
- 73.8% lice-free at day 15 (lower than spinosad or benzyl alcohol) 5
- Well tolerated with minimal adverse effects 5
- Reserved as third-line due to limited clinical experience and cost 5
Oral Ivermectin
- Single dose of 200 mcg/kg, repeated in 10 days 1
- Not FDA-approved for pediculosis 1
- Should not be used in children who weigh <15 kg due to risk of crossing blood-brain barrier 1
Treatments to Avoid
Lindane 1% should not be used as first-line treatment and only considered when all other treatments have failed. 1, 3
- Low ovicidal activity (30-50% of eggs not killed) 1
- Widespread resistance 1
- Serious safety concerns including seizure risk and neurotoxicity in children 1, 3
Who to Treat
- Only treat individuals with live lice or nits within 1 cm of the scalp 1, 3
- Examine all household members 1
- Treat family members who share a bed with the infected person 1, 3
- Do not treat based on itching alone or presence of nits >1 cm from scalp 2, 3
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 1, 2
- Remove items that cannot be washed from body contact for at least 72 hours (lice cannot survive off human body >2-3 days) 2, 3
- Fumigation of living areas is not necessary 2
Nit Removal (Optional)
- Nit removal is not necessary to prevent spread but can help decrease diagnostic confusion 3
- Apply vinegar or vinegar-based products to hair for 3 minutes before combing to help loosen nits 1
- Use fine-toothed nit comb after treatment 3, 4
Common Pitfalls and How to Avoid Them
Misdiagnosing Treatment Failure
- Most "resistance" is actually due to improper application 1, 2, 3
- Before assuming resistance, consider: misdiagnosis, noncompliance, reinfestation from untreated contacts, or improper technique 1, 3
- Post-treatment itching persists for days and is not a reason for retreatment—only retreat if live lice are seen 7-10 days after treatment 1, 2, 3
- Topical corticosteroids and oral antihistamines may help relieve post-treatment inflammation 1
Application Errors
- Using conditioning shampoo before permethrin prevents proper adherence 2
- Applying permethrin to soaking wet hair instead of damp, towel-dried hair 2
- Rinsing with hot water instead of warm water increases absorption 2
- Skipping the second permethrin application is the most common cause of treatment failure 2
- Using electric heat to dry hair after malathion application creates fire hazard 3, 4