What is the first-line treatment for head lice?

Treatment of Head Lice (Pediculosis Capitis)

First-Line Treatment Recommendation

Permethrin 1% cream rinse 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

Application Protocol for Permethrin 1%

The proper application technique is critical, as improper use is the most common cause of treatment failure—not resistance. 1, 3

Step-by-step application:

• Wash hair with a non-conditioning shampoo first (conditioning products prevent proper adherence) 3
• Towel dry until damp, not soaking wet 2, 3
• Apply permethrin 1% cream rinse thoroughly to the scalp, behind ears, and back of neck 1, 3
• Leave on for exactly 10 minutes—not longer or shorter 3
• Rinse with warm water over a sink (not hot water, to minimize absorption) 3
• Mandatory second application in 7-10 days to kill newly hatched nymphs, as permethrin has only 70-80% ovicidal activity 1, 3

Safety Profile

Permethrin has low mammalian toxicity and does not cause allergic reactions in patients with plant allergies. 1, 2 Post-treatment itching is common and normal—it represents an inflammatory response, not treatment failure, and should not prompt re-treatment unless live lice are seen 7-10 days after treatment. 1, 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 This indicates likely resistance, though you should first rule out improper application, misdiagnosis, noncompliance, or reinfestation from untreated contacts. 1, 2

Second-Line Treatment: Malathion 0.5%

Malathion is indicated when resistance to permethrin is documented or when first-line treatment fails despite correct use. 1

Application protocol:

• Apply to dry hair (unlike permethrin) 1, 2
• Allow to air dry naturally 1, 2
• Wash off after 8-12 hours 1, 2, 4
• Has the highest ovicidal activity (~98%) of all treatments, often requiring only a single application 1, 2
• Reapply in 7-9 days only if live lice are still present 1

Critical safety warning: Malathion contains 78% isopropyl alcohol, making it highly flammable—do not use near open flames, sparks, or while smoking. 2 It can cause severe respiratory depression if ingested. 1 Approved for children ≥6 months but contraindicated in children <24 months. 1

Alternative First-Line Option: Pyrethrins with Piperonyl Butoxide

Pyrethrins can be used as an alternative first-line treatment, applied to dry hair for 10 minutes, then rinsed, with a second application required in 7-10 days. 2, 4 However, efficacy is highly variable (13-75%) due to widespread resistance. 5

Third-Line Options

Spinosad 0.9% topical suspension achieves high cure rates with a single 10-minute application to dry hair. 1

Topical ivermectin 0.5% lotion is effective (73.8% lice-free at day 15) with a single application and minimal adverse effects, though it requires a prescription and is expensive. 6

Benzyl alcohol 5% kills lice by asphyxiation, requires repeat application in 7 days, and achieves >75% cure rates at 14 days. 1 Approved for children >6 months. 1

Treatments to Avoid

Lindane 1% should not be used due to low ovicidal activity (30-50%), widespread resistance, and serious safety concerns including seizure risk and neurotoxicity. 1, 2 It should only be considered when all other treatments have failed. 1

Household Management

• Examine all household members with a magnifying glass in bright light 4
• Only treat individuals with live lice or nits within 1 cm of the scalp 1, 2
• Treat family members who share a bed with the infected person 2
• Wash all clothing, bedding, and linens in hot water (>54°C/130°F) and dry on hot cycle for at least 20 minutes on the same day as treatment 2, 3, 4
• Soak combs and brushes in hot water for at least 10 minutes 2, 4
• 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 is not necessary 3

Nit Removal (Optional)

Nit removal is not necessary to prevent spread but can help decrease diagnostic confusion. 2 Apply vinegar or vinegar-based products to hair for 3 minutes before combing to help loosen nits. 1 Use a fine-tooth nit comb on slightly damp hair, working through 1-2 inch sections. 4

Common Pitfalls to Avoid

• Do not retreat based on itching alone—post-treatment pruritus persists for days and is an inflammatory response, not treatment failure 1, 2, 3
• Do not use conditioning shampoo before permethrin—it prevents proper adherence 3
• Do not skip the second application for permethrin or pyrethrins—it is mandatory due to incomplete egg kill 1, 3
• Consider improper application first before assuming resistance or treatment failure 1, 2
• Topical corticosteroids and oral antihistamines may help relieve post-treatment inflammation 1