What is the recommended treatment for pediculosis (lice infestation)?

Treatment of Head Lice (Pediculosis Capitis)

First-line treatment for head lice is permethrin 1% cream rinse applied to affected areas and washed off after 10 minutes, with a mandatory second application in 7-10 days. 1

First-Line Treatment: Permethrin 1%

• Apply permethrin 1% lotion to damp, shampooed hair (using non-conditioning shampoo) and towel-dried hair, leave on for 10 minutes, then rinse off 1
• A second application is mandatory in 7-10 days (preferably day 9) to kill newly hatched nymphs, as permethrin has incomplete ovicidal activity 2, 1
• Permethrin has extremely low mammalian toxicity and is safe for most patients 2
• Conditioners and silicone-based additives in modern shampoos impair permethrin adherence to hair shafts and reduce effectiveness—use only non-conditioning shampoos before application 2, 1

Alternative First-Line Option

• Pyrethrins with piperonyl butoxide can be used as an alternative first-line agent, applied to affected areas and washed off after 10 minutes, with repeat application in 7-10 days 2
• This option should be avoided in patients allergic to chrysanthemums 2

Second-Line Treatment: Malathion 0.5%

When permethrin or pyrethrins fail despite correct use, or when resistance is documented, malathion 0.5% is the treatment of choice. 1, 3

• Apply malathion 0.5% lotion to DRY hair in amount sufficient to thoroughly wet hair and scalp, paying particular attention to back of head and neck 4
• Allow hair to dry naturally with NO electric heat source and leave hair uncovered for 8-12 hours, then shampoo 4
• Malathion is highly flammable—the lotion and wet hair must not be exposed to open flames, electric heat sources, hair dryers, electric curlers, or smoking 4
• If lice are still present after 7-9 days, repeat with second application 4
• Malathion has approximately 98% ovicidal activity, making it highly effective 5
• Use only in children 24 months or older under direct adult supervision 2, 6
• Risk of severe respiratory depression if ingested—seek immediate medical attention for accidental ingestion 6, 4

Third-Line Treatment: Oral Ivermectin

• Oral ivermectin 200 mcg/kg (or 250 mcg/kg per CDC), repeated in 10-14 days, can be used as an alternative when topical treatments fail 2, 1
• Should NOT be used in children weighing less than 15 kg due to risk of crossing blood-brain barrier 1
• Ivermectin should be taken with food to increase bioavailability and epidermal penetration 2
• Has limited ovicidal activity, necessitating the second dose 2

Treatment to Avoid

Lindane 1% should only be used when other therapies cannot be tolerated or have failed, due to significant toxicity concerns including seizures and aplastic anemia. 1, 6

• Lindane has low ovicidal activity (30-50% of eggs survive) 1
• Should not be used in children under 10 years, persons weighing less than 50 kg, pregnant/lactating women, or those with extensive dermatitis 2, 6
• If used, apply for no more than 4 minutes then thoroughly wash off 2

Household Management

• Examine all household members; treat only those with live lice or nits within 1 cm of scalp 2, 1, 7
• Siblings who share a bed with the infested person should be treated even if no live lice are found 7
• Machine-wash and dry bedding and clothing using heat cycle, or dry-clean, or remove from body contact for at least 72 hours 2
• Clean hair care items used by infested person 7
• Fumigation of living areas is NOT necessary 2

Adjunctive Measures

• Nit removal after treatment is not necessary to prevent spread but is recommended for aesthetic reasons and to decrease diagnostic confusion 2
• Vinegar or vinegar-based products applied to hair for 3 minutes before combing help loosen nits attached to hair shaft 2, 1
• Topical corticosteroids and oral antihistamines may relieve post-treatment inflammation and itching 2, 1

Critical Pitfalls to Avoid

• Never initiate treatment without confirming diagnosis by finding live lice—nits alone more than 1 cm from scalp are insufficient for diagnosis 2, 1, 5
• When treatment appears to fail, consider improper application FIRST before assuming resistance—most "treatment failures" are due to incorrect use 2, 1, 7
• Other causes of persistent lice include: misdiagnosis, noncompliance with treatment protocol, reinfestation, or lack of ovicidal properties 2
• Do not use conditioning shampoos before permethrin application—they block adherence 2, 7
• Itching or mild burning after treatment is common and NOT a reason for re-treatment 1
• Children with head lice should NOT be excluded from school—they pose little risk to others and have likely had the infestation for a month or more by time of discovery 2

Special Populations

Pregnancy and Lactation

• Pregnant and lactating women should be treated with permethrin or pyrethrins with piperonyl butoxide 2
• Avoid lindane (associated with neural tube defects) and use malathion with caution 2

Eyelash Involvement

• Do not apply pediculicides to eyes—treat pediculosis of eyelashes by applying occlusive ophthalmic ointment or petroleum jelly to eyelid margins twice daily for 10 days 2