Lice (pediculosis)
Lice (pediculosis) is infestation of the scalp, body, or pubic region with human lice (Pediculus humanus capitis, corporis, or Pthirus pubis), diagnosed by finding a live louse or a viable nit close to the hair shaft, and treated with topical permethrin, malathion, or oral ivermectin plus environmental measures; body lice additionally vector epidemic typhus, trench fever, and relapsing fever.
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What this article covers
- Overview
Pediculosis is infestation of the human body with a blood-feeding louse, a wingless ectoparasitic insect; three species infest humans, each restricted to a specific body site: Pediculus humanus…
- Epidemiology
Head lice are common worldwide, especially among school-age children, with frequent classroom and household outbreaks; infestation occurs across all socioeconomic groups and does not reflect poor hygiene.
- Risk factors
Head-to-head contact and sharing of combs, brushes, hats, headphones, or hair accessories (head lice).
- Pathophysiology
Head lice attach to the scalp and cement their eggs (nits) firmly to the proximal hair shaft close to the scalp, where warmth supports egg viability; they feed directly on scalp skin.
- Clinical features
The hallmark is intense pruritus localized to the infested site, with visible lice or nits on examination, since a directly identified louse or viable nit is what establishes the diagnosis (see Diagnosis).
- Differential diagnosis
Scabies: see Scabies; intensely pruritic burrows in interdigital spaces, wrists, and periumbilical skin, confirmed by mites, eggs, or scybala on skin scraping, rather than lice or nits on hair shafts.
- Diagnosis
Pediculosis is a clinical diagnosis confirmed by directly identifying a live louse, or a viable (unhatched) nit located within about 1 cm of the scalp or skin surface; a nit found more than 1 cm from…
- Management
First, treat head or pubic lice with permethrin 1% cream rinse: apply to shampooed, towel-dried hair or the affected area, leave on for 10 minutes, then rinse; repeat the application in 9 to 10 days…
- Complications
Secondary bacterial skin infection (impetigo, folliculitis, cellulitis) from scratching, particularly with heavy or prolonged infestation.
- Prognosis
Excellent with appropriate pediculicide treatment combined with mechanical nit removal and environmental measures; most infestations resolve fully without sequelae.
- Prevention
Avoid head-to-head contact and sharing of combs, brushes, hats, and hair accessories to reduce head lice transmission.
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