What is the recommended treatment for lice (pediculosis)?

Treatment for Head Lice (Pediculosis Capitis)

Permethrin 1% lotion is the recommended first-line treatment for head lice, applied to damp, shampooed hair for 10 minutes, then rinsed, with a mandatory second application in 7-10 days. 1, 2

First-Line Treatment: Permethrin 1%

• Apply permethrin 1% cream rinse to damp hair that has been shampooed with a non-conditioning shampoo and towel-dried, leave on for 10 minutes, then rinse thoroughly over a sink (not shower) with warm water. 2, 1

• A second treatment on day 7-10 is essential because permethrin kills only 70-80% of eggs, and newly hatched nymphs must be eliminated before they mature and reproduce. 2, 1

• Many experts now recommend routine re-treatment on day 9 rather than waiting to see if live lice reappear, as this prevents treatment failure from being misinterpreted as resistance. 2

• Permethrin has extremely low mammalian toxicity and does not cause allergic reactions in patients with plant allergies, making it safer than pyrethrin-based products. 2, 1

Important Application Details

• Use a non-conditioning shampoo before application because conditioners and silicone-based additives in modern shampoos impair permethrin adherence to the hair shaft and reduce its residual protective effect. 2

• Rinse over a sink rather than in the shower to limit skin exposure, and use warm (not hot) water to minimize absorption from vasodilation. 2

Alternative First-Line Option: Pyrethrins with Piperonyl Butoxide

• Pyrethrins plus piperonyl butoxide can be used as an alternative first-line agent, applied to dry hair for 10 minutes then rinsed. 2, 3

• This option should be avoided in patients allergic to chrysanthemums or ragweed. 2

• Like permethrin, only 70-80% of eggs are killed, so a second treatment in 7-10 days is mandatory. 2, 3

• Resistance to pyrethrins has been reported, making permethrin the preferred choice. 2

Second-Line Treatment: Malathion 0.5%

• Malathion 0.5% lotion should be reserved for cases with documented resistance to permethrin or when first-line treatments fail despite correct application. 2, 1

• Apply to dry hair, allow to air dry naturally (do not use hair dryer), leave on for 8-12 hours, then wash off. 2

• Malathion has high ovicidal activity (kills more eggs than permethrin), but carries significant safety concerns: it is highly flammable due to high alcohol content and can cause severe respiratory depression if ingested. 2, 1

• Reapply in 7-10 days if live lice are still present. 2

Treatments NOT Recommended

Lindane 1%

• Lindane is no longer recommended by the American Academy of Pediatrics and is banned in California. 2

• The FDA warns it should only be used when patients cannot tolerate or have failed safer first-line treatments. 2

• Lindane has caused seizures in children, has low ovicidal activity (kills only 30-50% of eggs), and widespread resistance has been reported. 2

• It is contraindicated in neonates, children under 50 kg, pregnant/lactating women, and those with HIV or medications that lower seizure threshold. 2

Oral Ivermectin

• Oral ivermectin (200 mcg/kg repeated in 10 days, or 400 mcg/kg repeated in 7 days) is not FDA-approved for pediculosis and should not be used in children weighing less than 15 kg due to risk of crossing the blood-brain barrier. 2, 1

Sulfamethoxazole-Trimethoprim

• Not FDA-approved for lice treatment and carries risk of Stevens-Johnson syndrome, making it undesirable when safer alternatives exist. 2

Adjunctive Measures

Nit Removal

• After treatment, removal of nits (egg shells) is not necessary to prevent transmission but is recommended for aesthetic reasons and to reduce diagnostic confusion. 2, 1

• Use a fine-toothed nit comb on damp hair, working in small sections. 3

• Applying vinegar or vinegar-based products to hair for 3 minutes before combing helps loosen nits attached to the hair shaft. 2, 1

Household Management

• Examine all household members with a magnifying glass in bright light; treat only those with live lice or eggs within 1 cm of the scalp. 2, 1

• Treat family members who share a bed with the infested person. 2

• Machine wash clothing, bedding, and towels in hot water (above 54°C/130°F) and dry on the hottest setting for at least 20 minutes. 3

• Soak combs and brushes in hot water (above 54°C/130°F) for at least 10 minutes. 3

• Vacuum carpets, mattresses, and upholstered furniture. 3

• Items that cannot be washed can be sealed in a plastic bag for 72 hours or dry-cleaned. 3

Managing Post-Treatment Symptoms

• Itching or mild burning of the scalp after treatment is common and persists for many days after lice are killed—this is NOT a reason for re-treatment. 2, 1

• Topical corticosteroids and oral antihistamines can relieve post-treatment inflammation. 2, 1

Common Pitfalls

Treatment Failure vs. Resistance

When facing persistent lice after treatment, consider these explanations before assuming resistance: 2

1. Misdiagnosis (nits alone do not indicate active infestation—only live lice or viable eggs within 1 cm of scalp matter)
2. Noncompliance with treatment protocol (most common cause)
3. Reinfestation from untreated household contacts
4. Improper application (using conditioning shampoo, not leaving on long enough, rinsing in shower instead of sink)
5. Failure to retreat on day 7-10 (eggs not killed by first treatment hatch into nymphs)
6. True resistance (prevalence unknown but less common than above factors) 2, 1

School Policy

• Children with head lice should remain in school and not miss valuable school time. 2

• "No-nit" policies are not recommended because nits can persist after successful treatment with no risk of transmission. 2, 4

• The child should be discouraged from close head-to-head contact with others until treated. 2