Head Lice

Head lice (Pediculus humanus capitis) are obligate human ectoparasites that infest the scalp hair and feed on blood. Common in school age children (3 to 11 years), more in girls and in those with long hair; occurs in all socioeconomic groups and has no link with hygiene.

• Transmission: direct head-to-head contact; sharing combs, hats, pillows is a minor route. Lice cannot jump or fly; they survive 1 to 2 days off the head.
• Life cycle: females lay 5 to 10 eggs (nits) daily glued to hair shafts close to the scalp; nits hatch in 7 to 10 days; nymphs mature in 9 to 12 days; adults live about 30 days. Empty nit cases (white, farther from scalp) are not evidence of active infestation.
• Not a vector of disease in this setting. Complications: excoriation and secondary bacterial infection (impetigo), lymphadenopathy, sleep disturbance, psychological distress and school exclusion.
• Resistance to permethrin and malathion is widespread.

• Scalp itching (due to allergy to saliva; may appear 4 to 6 weeks after first infestation), papules and excoriation behind the ears and at the nape; secondary infection with crusting and cervical or occipital lymphadenopathy.
• Many children are asymptomatic.
• Diagnosis rests on finding a live moving louse (2 to 4 mm, grey brown).
• Red flags: widespread infected sores, cellulitis, fever, suspected neglect or abuse, eyelash infestation (pediculosis ciliaris, suspect sexual contact in children), persistent infestation after 2 proper treatments.

• Detection combing: wet hair with ordinary conditioner, comb through from the roots with a fine toothed (0.2 to 0.3 mm tooth spacing) louse detection comb, checking the comb after each stroke over a white surface, for at least 5 to 10 minutes; live lice confirm active infestation. Finding nits alone is not sufficient for treatment.
• Examine all household members and close contacts.
• Differentials: dandruff, seborrhoeic dermatitis, hair casts (move freely), dried hair spray, psoriasis, eczema, tinea capitis, impetigo, scabies.

• Treat only if live lice are found; treat all affected household members and contacts at the same time.
• Treatment options (apply and repeat after 7 days; check success with detection combing 2 to 3 days after the second application):
  • Dimeticone 4 percent lotion (physical action; no resistance): apply to dry hair and scalp, leave for 8 hours or overnight, then wash out with ordinary shampoo; repeat after 7 days. Safe from age 6 months and in pregnancy.
  • Malathion 0.5 percent aqueous liquid: apply to dry hair and leave for 12 hours (overnight), then wash out; repeat after 7 days; avoid under 6 months; flammable; contraindicated in broken skin and asthma caution.
  • Permethrin 1 percent cream rinse (applied to damp hair for 10 minutes then rinsed) or 5 percent cream for 8 to 14 hours (resistance common; second application at 7 to 10 days); avoid under 2 months.
  • Ivermectin 0.5 percent lotion applied to dry hair for 10 minutes, single application (age 6 months and over).
  • Spinosad 0.9 percent suspension applied to dry hair for 10 minutes (age 6 months and over); repeat after 7 days if live lice are seen.
  • Benzyl alcohol 5 percent lotion applied for 10 minutes, repeated after 7 days (age 6 months and over).
  • Oral ivermectin 200 micrograms/kg as a single dose, repeated after 7 to 10 days (for children weighing 15 kg or more and for resistant cases; not for pregnancy or breastfeeding).
• Wet combing (physical method, 'bug busting'): comb conditioned wet hair every 3 to 4 days for at least 14 days (until no lice found for 3 consecutive sessions); use for infants, pregnancy and those who prefer non-chemical options.
• Do not use insecticides for prevention; avoid repeated overuse of pediculicides.
• Environmental measures: wash combs and brushes in hot water; wash bedding and hats at 60 C or tumble dry or seal in a plastic bag for 2 days; vacuuming is enough for furniture; hot air or pesticide sprays are not needed.
• Treat secondary bacterial infection: topical mupirocin 2 percent ointment three times daily for 5 days, or oral flucloxacillin 12.5 to 25 mg/kg four times daily for 7 days for widespread infection.
• Itch: calamine lotion; antihistamine (cetirizine 2.5 mg twice daily at ages 1 to 5, 5 mg once daily at 6 to 11 years) for a short period.
• School: children do not need to be excluded; treatment should begin the same day. Inform the school and parents; check family members and friends.
• Persistent infestation: confirm adherence and application technique, rule out resistance, and switch to a different class of product.