Head Lice
Common ectoparasitic infestation caused by Pediculus humanus capitis, predominantly affecting primary school-aged children. Transmitted by direct head-to-head contact. Diagnosis requires identification of live lice by wet combing (detection combing). Treated with dimeticone 4% lotion or physical removal by wet combing ('Bug Busting').
Key Facts
Pediculus humanus capitis: obligate human ectoparasite; feeds on scalp blood Primary school children: peak age 4–11 years; girls > boys (due to play behaviour, not hair length) Detection combing (wet combing): gold standard diagnosis — systematic combing of conditioned wet hair with fine-toothed nit comb Dimeticone 4% lotion (Hedrin): first-line treatment — physical action (coats and suffocates lice); apply twice, 7 days apart Bug Busting: wet combing with conditioner on days 1, 5, 9, 13 — effective non-chemical alternative Resistance to malathion and permethrin: increasingly common in UK; dimeticone preferred Nits (egg cases): cemented to hair shafts; do NOT confirm active infestation (may be empty) Only treat if LIVE lice found: nits alone are not sufficient indication for treatment
Overview
Key Facts
Head lice infestation (pediculosis capitis) is extremely common in UK schoolchildren. It is not a sign of poor hygiene. Treatment should only be initiated when live lice are found. The emphasis has shifted from insecticide-based treatments to physical agents (dimeticone) and mechanical removal.
Epidemiology
- Very common: affects ~10–20% of primary school children at any time
- Peak age: 4–11 years
- Girls > boys (~3:1)
- No social class or hygiene association
- Year-round incidence; no seasonal peak in UK
Aetiology
- Pediculus humanus capitis: wingless insect, 2–3 mm long
- Transmission: direct head-to-head contact (NOT via hats, combs, or pillows — lice die within 24–48 hours off the host)
- Life cycle: egg → nymph → adult (~3 weeks); adult lifespan ~30 days; female lays 6–8 eggs/day
- Nits (empty egg cases) cemented to hair shaft ~1 cm from scalp
Pathophysiology
- Louse pierces scalp skin → feeds on blood → injects saliva containing anticoagulant
- Sensitisation to saliva → pruritus (takes weeks to develop after first infestation)
- Excoriations → secondary bacterial infection (impetigo)
Clinical Presentation
Typical Presentation
- Scalp pruritus: most common symptom; may be absent in early infestation
- Worse behind ears and nape of neck: preferred feeding sites
- Excoriations and eczematisation from scratching
- Live lice: 2–3 mm, grey-brown wingless insects (move rapidly, hard to spot)
- Nits: white/brown oval egg cases attached to hair shafts — NOT diagnostic of active infection
- Secondary impetigo: crusted, golden lesions from scratched excoriations
Occipital and Post-Auricular Lymphadenopathy
- Reactive, tender nodes — common with active infestation
Red Flags
- Widespread secondary infection requiring antibiotics
- Severe excoriations causing scarring
- Child safeguarding: persistent, severe, untreated infestation may (rarely) raise concerns
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Dandruff (seborrhoeic dermatitis) | Diffuse flaky scale, easily brushed off | Clinical |
| Hair casts (pseudonits) | White cylindrical deposits; slide along hair shaft | Microscopy |
| Nit cases (no active infestation) | Empty nit cases >1 cm from scalp | Detection combing — no live lice |
| Scalp psoriasis | Thick silvery plaques, well-defined | Clinical, biopsy |
| Piedra | Hard nodules on hair shaft (fungal) | Microscopy, culture |
Diagnosis / Investigation
Bedside
- Detection combing (wet combing): gold standard
- Apply conditioner to wet hair → comb systematically with fine-toothed plastic detection comb (0.2–0.3 mm tooth spacing)
- Check comb after each stroke for live lice and nymphs
- More sensitive than dry visual inspection (4× more effective)
Microscopy
- Live louse examination: identifies species (rarely needed)
- Nit examination: viable nit is brown, close to scalp; hatched nit is white, further from scalp
Bloods
- Not required
Special Tests
- Not required for diagnosis
Management
Non-Pharmacological
- Wet combing (Bug Busting method): effective alternative to chemical treatment
- Apply conditioner → systematic combing with fine-toothed comb → wipe comb on tissue
- Perform on days 1, 5, 9, 13 (covers full life cycle)
- Continue until no live lice found on 3 consecutive sessions
- Only treat if LIVE lice found: finding nits alone does not require treatment
- Check household contacts: treat only those with confirmed live lice
- School exclusion: NOT recommended by Public Health England
Pharmacological
- Dimeticone 4% lotion (Hedrin): first-line — apply to dry hair, leave 8 hours (or overnight), wash out; repeat at day 7
- Physical mode of action: coats and suffocates lice; no resistance issues
- Dimeticone 92% (Hedrin Once): spray gel, apply for 8 hours; single application may suffice
- Isopropyl myristate/cyclomethicone solution (Full Marks): physical action; apply for 10 minutes, comb out dead lice; repeat at day 7
- Malathion 0.5% aqueous liquid: second-line — apply to dry hair, leave 12 hours; repeat at day 7; resistance increasingly common
- Permethrin: no longer recommended as first-line due to widespread resistance in UK
Important Notes
- Always repeat treatment at day 7 to kill newly hatched lice from surviving eggs
- Combination of treatment + combing improves success
- Contact tracing: check and treat household members with confirmed live lice
Referral Criteria
- Rarely needed; manage in primary care
- Dermatology: if diagnostic uncertainty or secondary complications
- School nursing: for recurrent outbreaks — education and support
Prognosis
- Excellent with appropriate treatment — cure rates >90% with dimeticone or thorough wet combing
- Treatment failure: usually due to reinfestation from untreated contacts, poor application technique, or treatment resistance
- Resistance: increasing to malathion and permethrin; dimeticone and physical methods unaffected
- Secondary infection: responds well to appropriate antibiotics
- Psychological impact: significant distress to children and parents; reassurance important
Other Relevant Information
Head Lice Treatment Comparison
| Treatment | Mode of Action | Application | Resistance |
|---|---|---|---|
| Dimeticone 4% (Hedrin) | Physical (suffocation) | 8 hours, repeat day 7 | None |
| Dimeticone 92% (Hedrin Once) | Physical (suffocation) | 8 hours, single/repeat | None |
| Isopropyl myristate (Full Marks) | Physical (dissolves wax) | 10 mins, repeat day 7 | None |
| Malathion 0.5% | Chemical (AChE inhibitor) | 12 hours, repeat day 7 | Increasing |
| Wet combing (Bug Busting) | Mechanical removal | Days 1, 5, 9, 13 | None |
Bug Busting Schedule
| Day | Action |
|---|---|
| Day 1 | Wet comb — remove all lice |
| Day 5 | Wet comb — catch hatched nymphs |
| Day 9 | Wet comb — catch any remaining |
| Day 13 | Wet comb — confirm clearance |