D.R. Thomas, MD, FRCPC1; A.H.Y. Cho, RPh, BScPharm2

1 Department of Dermatology and Skin Science, University of British Columbia, Vancouver, BC, Canada
2 Skin Care Centre Pharmacy, Vancouver, BC, Canada


Head lice infestations (Pediculosis humanus capitis) are most prevalent during childhood in industrialized countries. It is estimated to occur in about 1-3% of children aged 6-12 years.1 Greater susceptibility is associated with girls, which is likely attributed to close contact play and the sharing of objects.2 Infestations are caused by direct physical contact with humans or fomites carrying live lice. Head lice infestations do not pose health risks, nor are they indicative of poor hygiene. Instead, active infestations signal the onset of a potentially widespread nuisance in schools and homes, and may subject affected individuals and their family members to stigmatization within their community. Diagnostic accuracy, decontamination, and topical therapy are required for containment and eradication.

Facts on Head Lice

  • Adult lice are 2-4 mm long (about the size of a sesame seed). These wingless insects cannot jump or fly. Hence, hair-to-hair contact represents the primary mode of transmission.
    • Lice can crawl rapidly (about 6-30 cm per minute).
    • They can adapt their colour to their surroundings, making detection by visual inspection difficult.
    • Lice survive by sucking blood from their host every 3-6 hours and they cannot miss several consecutive meals.2
    • After mating, an adult female louse can lay 5-6 eggs daily for 30 days.3
  • Eggs (nits) are laid on the hair shaft closest to the scalp.
    • Nits are very small and oval-shaped, and they range in colour from white to tan or silver to grey.
    • Nits are located near the scalp owing to the warmer temperature and close proximity to their eventual food supply.
  • Nymphs (hatched immature lice) require 9-12 days to reach adulthood.


  • Most infestations are asymptomatic, but persistent itching occurring near the back of the head and/or around the ears is commonly the first noticeable symptom. Sleeplessness, red marks, excoriations, and rash can also occur.
  • Pruritis may be experienced 2-6 weeks after the first infestation; itching may occur sooner (1-2 days) in future infestations due to prior sensitization to antigens present in lice saliva during the initial exposure.


Early detection of head lice is important for reducing its communicable potential. Diagnositic accuracy can be challenging
and requires experience and expertise, as lice can readily evade detection by their rapid mobility and minimal visibility.
Additionally, nits can resemble dandru., scabs, hair spray droplets, or other debris.4

  • An active infestation is de.ned by the presence of 10 or more live lice.5
  • The discovery of nits alone without live lice does not indicate infestation; about 10-30% of nits do not hatch.6
  • Overdiagnosis by healthcare professionals is common, whereby extinct or inactive infestations are determined to be
  • active infestations and pharmacologic intervention is unnecessarily initiated.5
  • Once an active infestation has been confirmed, alert and screen everyone in the household and close contacts.

Methods of Detection

Although visual inspection is easier to perform, wet combing with conditioner (WCWC) remains the most reliable method of detection.1,6

WCWC Method for Head Lice Detection6

  • Apply a liberal amount of conditioner (white is best) to dry hair, soaking strands from scalp to ends.
  • Remove tangles with a regular bright light-coloured comb.
  • Start behind the ears and comb each section of hair.
  • Place the lice comb (a special fine-tooth comb) against the scalp and pull to the end of the hair.
  • Check the comb for lice after each pull.
  • Wipe the comb with a tissue each time and look for lice.
  • Place the tissue in a plastic bag.
  • Check all the hair over the entire head.
  • Repeat combing every section of hair at least 5 times.
  • When finished, tie the plastic bag with the soiled tissues and discard in the garbage.
  • If live lice are detected, all traces of conditioner must be washed from the hair prior to treatment.

Manual Removal

Manual removal of lice and nits is recommended for children Manual removal and daily lice combing serve as useful adjunctive measures. These nonpharmacologic approaches aid in reducing pediculicidal resistance, which is a concern in topical insecticidal use.

Environmental Decontamination

Because lice can survive away from a human host for 3-4 days, implementing fomite control strategies can eliminate potential sources of transmission and minimize reinfestation.

  • Personal items used or worn by an infested person during the 3 days before treatment should be machine laundered in hot
  • water (e.g., linens, blankets, pillows, stuffed toys, and clothing), then placed in a dryer using a hot setting for 20 minutes.
  • Objects that cannot be washed should be stored in a tightly-wrapped plastic bag for 2 weeks or in a freezer for 24 hours.
  • Soak combs (including lice comb) and hairbrushes in very hot water for 20 minutes or in rubbing alcohol for 1 hour.
  • Vacuum carpets, furniture, and mattresses that the infested person came into contact with.
    • Extensive cleaning is unnecessary as the survivability of head lice away from the scalp is limited.
  • Insecticidal sprays have not been shown to be effective.
  • Children should be permitted to return to school after appropriate treatment; strict no-nit policies are unnecessary.4,5,7

Topical Treatment

Topical treatment (Table 1) is recommended only when live lice are found. To prevent reinfestation, it is advisable to treat all infested family members and close contacts immediately and on the same day.6

Key Points of Topical Treatment

  • Permethrins (synergized pyrethrins) are considered first-line therapies and most preparations are available OTC.
  • Available pediculicides are not 100% ovicidal. Consequently, for all topical therapies, two treatments (7-10 days apart) are necessary to eradicate the nymphs that are hatched from nits not killed by the first treatment.
  • Depending on the pediculicide, specific application to either wet or dry hair is required.
  • Adequate saturation and treatment duration are essential for penetration of lice and nits by the active agent.
  • The medication should be applied not only to the scalp and along the hair shaft, but also to the back of the ears and neck.
  • Patients should not wash their hair for 1-2 days after the treatment is rinsed off.
  • The presence of live lice after treatment does not indicate failure, as it can take up to 24 hours for the parasites to die.
  • The most common side-effects from topical therapies include itchiness, mild skin irritation, and redness.
    • Post-treatment itching is not an indication of reinfestation.
  • Many proposed alternative or natural treatments, such as tea tree oil, petroleum jelly, peanut butter, and mayonnaise have not been clinically proven to be effective.
Topical AgentDetails of Use
  • Wash hair with shampoos that are free of conditioner and silicone; towel dry until hair is almost dry
  • Apply product to hair, scalp, behind ears, and neck; leave for 10 minutes, rinse with cool water over a sink (not in the shower or bath)
  • Comb wet hair with nit comb to remove dying lice and nits
  • Approved for use in persons >2 years of age
  • Compatible with pregnancy and breastfeeding; low risk of toxicity
  • Does not cause allergic reactions; may cause itching or mild burning sensation of the scalp
Pyrethrin + Piperonyl Butoxide
  • Apply to completely DRY hair
  • Leave on for 10 minutes, then add water to form lather
  • Rinse with cool water over a sink; do not use conditioner
  • Approved for use in persons >2 years of age
  • Probably compatible with pregnancy and breastfeeding; low risk of toxicity
  • Do not use if there is a known allergy/sensitivity to chrysanthemum or ragweed
  • Second-line treatment
  • Apply to DRY hair and leave for 5 minutes (avoid skin contact beyond the scalp), rinse with cool water over a sink (not in the shower or bath)
  • Neurotoxic at high doses or with repeated exposure
  • Contraindicated in neonates, young children (
  • Resistance has been observed; may cause scalp irritation
Isopropyl Myristate + Cyclomethicone
  • Nonpediculicidal OTC treatment approved by Health Canada in 2006
  • Second-line to permethrin; may be tried first if a noninsecticide is favoured
  • Dehydrates and kills lice by dissolving the exoskeleton
  • Apply to DRY hair and leave on for 10 minutes, then rinse with warm water
  • Indicated for individuals >4 years of age
  • Potential for local irritation
Table 1: Topical treatments for active head lice infestations4,6,8

Treatment Failure

The most common reasons for treatment failure include:

  • Misdiagnosis
  • Improper use (e.g., not saturating hair from scalp to ends or not leaving the product on long enough)
  • Not repeating the treatment after 7-10 days or reapplication too soon after initial application
  • Pediculicidal resistance
  • Inadequate manual removal of nits
  • Repeat exposure to lice (reinfestation)

Improper management of an active infestation poses considerable costs to a family as:8

  • the child may not be permitted to attend school and may be ostracized and stigmatized.
  • the parent may be required to take time off from work or pay for alternate care.
  • the family must commit time and financial resources for eradication and prevention of reinfestation.


Although head lice infestation is not as prevalent in Canada as in developing countries, it remains a common communicable problem that carries substantial costs, both financial and social, for affected individuals. Given their favourable safety and efficacy profiles, permethrins and synergized pyrethrins remain first-line treatments for Pediculosis capitis.3,4,6,7 Diagnositic accuracy and appropriate management, as well as education aimed at reducing transmission, are central for eradication and minimizing the suffering and treatment-related costs for those impacted.


  1. Jahnke C, et al. Arch Dermatol 145(3):309-13 (2009 Mar).
  2. Meinking TL. Curr Probl Dermatol 11(3):73-118 (1999 May-Jun).
  3. Burkhart CN. Lancet 361(9352):99-100 (2003 Jan 11).
  4. Centers for Disease Control and Prevention. Fact sheet: head lice. Available at: http://www.cdc.gov/lice/head/factsheet.html. Accessed August 12, 2009.
  5. Position statement from Infectious Diseases and Immunization Committee, Canadian Paediatric Society. Paediatr Child Health 13(8):692-704 (2008 Oct).
  6. District Health Authority Public Health Services of Nova Scotia. Guidelines for treatment of pediculosis capitis (head lice), August 2008.
  7. Diamantis SA, et al. Dermatol Ther 22(4):273-8 (2009 Jul-Aug).
  8. Boivin M. Webmodule: Skin clinic vignettes – infestations. Head lice and scabies. rxBriefCase (2009 May).