CPS Statement: Head Lice Infestations: A Clinical Update

CPS Statement: Head Lice Infestations: A Clinical Update

The following was adapted from the Canadian Paediatric Society's statement on "Head Lice Infestations: A Clinical Update".  Please see the full statement for the full recommendations from the Canadian Paediatric Society.  

What are head lice?

  • adult louse are six-legged, wingless insects that feed off of blood from the human scalp (2-4mm in length)
  • found in close proximity to l the scalp where they obtain food, warmth, shelter and moisture
  • adult females mate, and then produce 5-6 eggs per day for 30 days
  • nit = louse eggshell (either containing a larva, or remaining after that larva hatches)
    • viable nits most often found within 0.6cm of the scalp, as they require these warmer temperatures to hatch successfully

NOTE: it is important to distinguish that head lice infestations are NOT a representation of poor hygiene, and are not a significant health hazard

Head Lice Infestation (Pediculosis)

  • most common in school-aged children
  • usually involves less than 10 live lice
  • can be asymptomatic for weeks
  • itching is NOT a cardinal feature
    • instead it represents sensitization to antigenic components (usually takes 4-6 weeks to occur in a first-time infection)


  • occurs by direct hair-to-hair contact only (lice crawl rapidly, but do not fly)
  • pets are not vectors for human head lice


  • definitive diagnosis only occurs with detection of a live louse (requires experience)
  • nits indicate presence of a past or ongoing infestation, but are not definitive of an active infestation




Summary of Evidence

Topical insecticides


Permethrin 1%


  • None are 100% ovicidal – recommend reapplication in 7-10days.
  • Toxic substances with minimal cutaneous absorption, but still prescribe with recommendations to minimize body exposure.
  • Lindane a second-line agent because of potential for neurotoxicity and bone marrow suppression.

NOTE: scalp itchiness can occur following use of these topical therapies, avoid misinterpreting this as resistance to therapy

Oral agents



  • Limited evidence to support use

Wet combing

Mechanical removal, combing wet hair with a fine toothed comb.

  • Studies show none to minimal significant benefit.

Other Important issues:

Home remedies

  • Little evidence exists to support home remedies such as mayonnaise, olive oil, margarine, thick hair gel etc.

Exclusion from school/daycare

  • There is no medical rationale for exclusion from school or daycare.  Instead appropriately educate and recommend avoidance of head-to-head contact until treated.

Environmental decontamination

  • Head lice are not viable at distances away from human scalp, so efforts at environmental decontamination can reasonably be limited to items in direct contact with hair such as hats, pillowcases, brushes and combs. (Wash in hot water at dry with hot dryer for 15 minutes, OR store in an occlusive plastic bag for 2 weeks.) 

Reference: Finlay, J and MacDonald, N.E. (2008). Head lice infestations: A clinical update. Paediatric Child Health, 13(8), 692-696. Reaffirmed Feb 1, 2014.

Last updated by PedsCases on February 10, 2015. 

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