Head Lice

Head lice are small wingless insects (Pediculus humanus capitis) that infest the scalp and hair shafts, feeding on human blood. They are common in children worldwide 🌍 and spread mainly by direct head-to-head contact.

🧬 Aetiology & Life Cycle

• 🪳 Adult louse: ~2–3 mm long, grey-white or brown; survives up to 30 days on scalp.
• 🥚 Nits (eggs): oval, ~0.8 mm, cemented to hair shafts close to scalp. Hatch in 7–10 days.
• 🧒 Transmission: head-to-head contact (combs/hats less significant).
• ❌ Not linked to poor hygiene or socioeconomic status (common myth).

🩺 Clinical Features

• Itchy scalp (pruritus) – delayed hypersensitivity reaction to louse saliva 🩸.
• Excoriations, secondary bacterial infection (impetiginisation).
• Nits visible on hair shafts – live eggs within 1 cm of scalp; empty casings further away.
• Cervical lymphadenopathy in heavy infestations.
• Often asymptomatic in early infestation.

🔎 Diagnosis

• 🎯 Gold standard: detection of a live louse by careful examination.
• 🪮 Detection combing: fine-toothed comb on wet, conditioned hair improves sensitivity.
• Note: Nits alone ≠ active infestation (may be old/empty).

⚖️ Differential Diagnoses

• Dandruff (scaly white flakes, easily dislodged).
• Hair casts.
• Scalp psoriasis or seborrhoeic dermatitis.
• Other ectoparasites (fleas, scabies, body lice).

💊 Management (UK / NICE)

Aim: eradicate lice, avoid unnecessary treatment, prevent reinfestation.

• 🪮 First-line: Wet combing with detection comb + conditioner, repeated every 3–4 days for 2 weeks (minimum 4 sessions).
• 💊 Insecticidal options (if combing fails):
  • Dimeticone lotion (physical action – coats and suffocates lice).
  • Isopropyl myristate / cyclomethicone sprays.
• 🔥 Malathion lotion (0.5%) – less used due to resistance.
• 🚫 No prophylactic treatment of contacts unless live lice found.
• 👨‍👩‍👧 Treat all affected family members simultaneously.

🧼 Prevention & Education

• Encourage regular detection combing in children at risk (e.g. school outbreaks).
• Explain that lice are not linked to poor hygiene.
• Close contacts should be checked but only treated if infestation confirmed.
• Wash bedding/clothes used in previous 48 hours in hot cycle if practical (though lice survive briefly off scalp).

🚨 Complications

• Secondary bacterial infection (impetigo).
• Cervical lymphadenitis.
• Psychological distress, stigma in children/parents.

📚 Exam Pearls

• Diagnosis requires live lice, not just nits 🪳.
• Wet combing is first-line in UK children; reserve chemicals if unsuccessful.
• Dimeticone is safe in asthma/eczema; malathion less used (resistance, smell).
• No exclusion from school needed once treatment started 🏫.

🔗 References

• NICE CKS – Head Lice
• NHS – Head Lice and Nits
• DermNet NZ – Head Lice

🐛 Case 1 — School-Aged Child

A 7-year-old girl is brought to the GP by her mother with persistent scalp itching, worse at night. Examination reveals live lice and nits attached to the hair shafts behind the ears and at the nape of the neck. 💡 Head lice are common in school-aged children and spread by direct head-to-head contact. Diagnosis is confirmed by detection combing. Management includes physical removal with a fine-toothed comb and topical treatments such as dimeticone or malathion, with advice on checking household contacts.

🐛 Case 2 — Recurrent Infestation in a Teenager

A 14-year-old boy presents with recurrent itchy scalp despite over-the-counter shampoos. Close examination shows adult lice and excoriation marks. He shares sports equipment and has siblings with similar symptoms. 💡 Recurrent infestation often reflects inadequate treatment or untreated contacts. Reinfection can be prevented by systematic wet combing, treating all affected household members simultaneously, and reinforcing education that lice are not a sign of poor hygiene. Second-line pediculicides may be required if resistance is suspected.