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Updated: Oct 20 2021


  • Snapshot
    • A 6-year-old girl is brought to the pediatrician's office for an "itchy" head. She is actively scratching her hair. She has no significant past medical history. Her mom reports that they live in a homeless shelter with crowded living conditions. Several other children there also were seen scratching their head. Physical exam reveals several non-viable nits > 1 cm away from the base of the hair shaft and viable nits < 1 cm away from the base of the hair shaft. She is given topical permethrin.
  • Introduction
    • Clinical definition
      • a very common ectoparasitic infestation of the scalp (pediculosis capitis or head lice) or pubic hair (pediculosis pubis or pubic lice)
        • pubic lice is also known as crabs
      • can also involve other hair-bearing areas, such as eyebrows or eyelashes
    • Epidemiology
      • incidence
        • common
      • demographics
        • head lice
          • girls > boys
          • healthy children, regardless of hygiene
          • adults with poor hygiene
          • less common in African Americans
        • pubic lice
          • teenagers and young adults
          • men who have sex with men
          • men > women
      • risk factors
        • household contact with infected children
        • overcrowded living conditions
    • Etiology
      • head lice
        • infestation with head louse Pediculus humanus capitis
        • transmitted via hair-to-hair direct contact
      • pubic lice
        • infestation with crab louse Pthirus pubis
        • transmitted via close physical or sexual contact
    • Pathogenesis
      • the life cycle of louse is the nit (egg), nymph (immature louse), and adult louse
      • females lay nits (eggs) that are attached to the hair
        • the farther away the nit from the base of the hair shaft, the older the infection
        • nits > 1 cm away from hair shaft may indicate an old, not active, infection
      • pruritus is caused by injection of saliva in the skin
    • Associated conditions
      • sexually transmitted diseases (in cases of pubic lice)
      • scabies
    • Prognosis
      • pruritus may linger until 10 days after treatment
      • may recur
  • Presentation
    • Symptoms
      • scalp or genital itching
      • a sensation of “crawling”
      • conjunctivitis if there is eyelash infestation
      • may be asymptomatic
    • Physical exam
      • examine by wet combing using a fine-tooth comb
      • live lice may be appreciated
      • more commonly, nits are found along at the base of the hair shaft
        • nits < 1 cm is considered viable
        • often appear white
      • secondary skin lesions from scratching
        • excoriations or impetigo
  • Studies
    • Microscopic examination
      • may identify lice or nits on hair shafts
    • Making the diagnosis
      • most cases are clinically diagnosed
  • Differential
    • Scabies
    • Chiggers
  • Treatment
    • Management approach
      • patients with head lice are treated with topical pediculicide initially or oral ivermectin in cases of treatment failure
        • children do not have to be kept from school
        • household members should be screened for head lice
    • Conservative
      • no shared clothing or hair accessories
      • wash all linens and clothing that could’ve come into contact with lice
    • Medical
      • occlusive topical agent
        • indications
          • for children with eyelash infestation
        • modalities
          • petroleum jelly
      • topical pediculicide
        • indications
          • for all patients
        • drugs
          • permethrin
          • ivermectin
          • dimethicone
      • oral ivermectin
        • indications
          • topical treatment failure
  • Complications
    • Secondary bacterial infection from scratching
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