Recommended Treatment for Head Lice
Permethrin 1% cream rinse (Nix) is the first-line treatment for head lice, applied to damp, towel-dried hair for exactly 10 minutes, then rinsed off, with a mandatory second application 7-10 days later. 1, 2, 3
Application Technique
- Shampoo hair first with a non-conditioning shampoo (not regular shampoo with conditioner, as silicone-based additives prevent proper adherence to the hair shaft) 4, 2
- Towel dry hair until damp, not soaking wet 2, 3
- Apply permethrin 1% cream rinse thoroughly to the scalp and hair 2
- Leave on for exactly 10 minutes—not longer or shorter 2
- Rinse with warm water over a sink to minimize skin absorption 1, 2
- Repeat application in 7-10 days (preferably day 9) is mandatory, as permethrin has only 70-80% ovicidal activity, meaning 20-30% of eggs survive the first treatment 4, 1, 2, 3
Safety Profile
- Permethrin has extremely low mammalian toxicity and is the least toxic pediculicide available 4
- Does not cause allergic reactions in patients with plant allergies (unlike pyrethrins) 4, 3
- Reported adverse effects are minimal: mild pruritus, erythema, and edema 4
- Safe for children 2 months and older 5
Critical Pitfalls to Avoid
- Most treatment "failures" are due to improper application, not resistance—consider misdiagnosis, noncompliance, or incorrect technique before assuming resistance 1, 3
- Do not use conditioning shampoo before application, as it prevents permethrin from adhering to hair 2
- Post-treatment itching is normal and NOT a sign of treatment failure—itching can persist for days to weeks due to inflammatory response to dead lice 1, 2, 3
- Only retreat if live lice are seen 7-10 days after treatment, not based on itching alone 2, 3
- Do not skip the second application—it is mandatory due to incomplete egg kill 2, 3
When First-Line Treatment Fails
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 1
- Malathion 0.5% kills permethrin-resistant lice approximately 10 times faster and has the highest ovicidal activity (~98%) of all available treatments 1
- Apply to dry hair, allow to air dry naturally, then wash off after 8-12 hours 1, 3
- Warning: Malathion contains 78% isopropyl alcohol and is highly flammable—avoid open flames, hair dryers, and smoking during use 1, 3
- Approved for children 6 months and older 1
Household and Environmental Management
- Examine all household members and only treat those with live lice or nits within 1 cm of the scalp 1, 3
- Treat family members who share a bed with the infected person 3
- 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, as lice cannot survive off the human body for more than 2-3 days 2, 3
- Fumigation of living areas is not necessary 2
Alternative First-Line Options
- Spinosad 0.9% topical suspension achieves high cure rates with a single 10-minute application to dry hair 1
- Pyrethrins with piperonyl butoxide can be used as an alternative, applied to dry hair for 10 minutes, requiring a second application in 7-10 days 3