Head lice

Overview

•Scalp itching - worst behind ears and nape of neck

•Sensation of movement in hair - characteristic symptom

•Nits - white/yellow-white oval casings firmly cemented to hair shafts; do NOT brush off (unlike dandruff)

•Live lice - 1-3 mm, tan to grey-brown; confirms active infestation

Investigations

•Clinical diagnosis - no investigations required

•Detection combing - fine-toothed nit comb on wet, conditioned hair; live lice confirm active infestation; empty nit casings alone do NOT confirm active infestation

Management

•Treat only individuals with confirmed live lice - household contacts should be checked and treated only if live lice found; prophylactic treatment of asymptomatic contacts is NOT recommended

⚠️
Treatment failure with malathion - consider three causes before switching: (1) resistance - switch to dimeticone or wet combing; (2) reinfection from untreated school/home contacts; (3) incorrect application. Do not repeat malathion if resistance suspected.

Head lice treatment options
FeatureWet combingDimeticone 4% lotionMalathion 0.5% liquid
TypeNon-insecticidePhysical insecticideChemical insecticide
LineFirst-lineFirst-lineSecond-line
MethodConditioner + fine comb, root to tip; every 3-4 days for ≥2 weeksApply to dry hair, leave 8 hours, wash off; repeat at day 7Apply to dry hair, leave 12 hours, wash off; repeat at day 7
When to usePatient/parent preference for non-chemical; all ages including infants, pregnancy, breastfeedingPreference to avoid chemical insecticide; pregnancy/breastfeeding; asthma/eczema; age ≥6 monthsAfter wet combing failure and dimeticone not preferred; not for children <2 years
Resistance riskNoneUnlikely (physical mechanism)Documented UK resistance

Feature	Wet combing	Dimeticone 4% lotion	Malathion 0.5% liquid
Type	Non-insecticide	Physical insecticide	Chemical insecticide
Line	First-line	First-line	Second-line
Method	Conditioner + fine comb, root to tip; every 3-4 days for ≥2 weeks	Apply to dry hair, leave 8 hours, wash off; repeat at day 7	Apply to dry hair, leave 12 hours, wash off; repeat at day 7
When to use	Patient/parent preference for non-chemical; all ages including infants, pregnancy, breastfeeding	Preference to avoid chemical insecticide; pregnancy/breastfeeding; asthma/eczema; age ≥6 months	After wet combing failure and dimeticone not preferred; not for children <2 years
Resistance risk	None	Unlikely (physical mechanism)	Documented UK resistance

📌
NOT recommended by NICE (insufficient evidence): coconut oil shampoos, tea tree oil and other essential oils, electric nit combs, head lice repellent sprays.

🎯
Dimeticone is a physical (not chemical) insecticide - if a parent wants to avoid insecticides entirely, only wet combing qualifies. If they want to avoid chemical insecticides, dimeticone is acceptable.