The (Lice) Drugs Don’t Work … Or Do They?

For those of us in the northern hemisphere, summer is drawing to an end and that means back to school – and the annual wave of panic about head lice. It seems that cramming hundreds of children together in one building leads to lice outbreaks, panicky teachers, and distraught parents. Right on schedule, in last week’s Globe and Mail under the heading “Medical Rethink” was the article Chemical Lice Treatments May Not Work. The article isn’t available at their website, probably because it’s copied nearly verbatim from the Wall Street Journal, where it’s online with the less provocative title Tired of Nit-Picking? Lice Are Peskier Than Ever.

The article was based on the newly-updated American Academy of Pediatrics Clinical Report on Head Lice. Well since I blogged about head lice about a year ago, I thought I’d better review the new guidance and see if my interpretation of the evidence needs to be updated. Science-based practice is always tentative, and subject to change if persuasive evidence emerges. So what’s up in the new report?

I’ve covered off the broad treatment strategy for head lice in my previous post. The key point I made is that you don’t need any drugs at all to treat head lice. There are chemical and non-chemical options, and both work – as long as you’re fastidious. Chemicals kill the lice, or you can physically remove them with a comb. Both strategies need to be repeated over several days. Slip up with either approach, and the lice won’t be eliminated. So what’s the new report say about the chemical treatments? Is a new strategy warranted?

To be clear, the AAP report isn’t a systematic review. It’s not even clear a systematic literature search was done. There are dozens of people credited in the document, but the preparation process isn’t documented at all. Still, I consider the AAP a credible organization, so I’ll consider their advice (let’s call it expert opinion, or a clinical review) seriously. If the drugs don’t work, I’ll recommend what does.

The key point, and the biggest change from what I’ve seen advocated in the past, is the tentative suggestion of a three-cycle chemical treatment. Previous guidance has always been to administer a chemical lice treatment on day zero, and then repeat the same treatment in 7-10 days. The AAP report now suggest the second dose, specifically on day 9 “is optimal”, and that a different, three-time dosing schedule(days 0, 7, and 13 to 15) may be considered. The reason? Lice resistance to treatment.  As the treatments kill live lice, but not eggs, one treatment never works, but disappointingly, two doesn’t always seem to, either. What data exist to suggest resistance is worsening? The AAP document states,

The prevalence of resistance has not been systematically studied but seems to be highly variable from community to community and country to country.

And that’s where I’m frustrated with the treatment of head lice. Without systematic evaluation, I suspect the “resistance patterns” within any country are based mainly on anecdote. Ask the local pharmacist, and they’ll know which products are associated with treatment success and which are leaving parents frustrated – based on what customers tell them. But because application technique, repeat doses, and proper follow-up are so essential to treatment success, we have no idea if treatment failures that are reported are due to resistance or usage errors. So it could be the drugs work fine – they’re just not being used properly.

The report suggests permethrin 1% (Nix) and pyrethins plus piperonyl butoxide (RID (USA), R&C (Canada)) as the chemical treatments of choice. The report doesn’t give much ink to isopropyl myristate (Resultz) which is available in Canada, but not in the United States. My personal opinion is that this product is also an acceptable option for first-line treatment. Consult the report for full details about each treatment.

The report also mentions a few “natural” products (yes, they put “natural” in quotes). It properly notes that these products are not required to meet FDA efficacy and safety standards (the same applies to Canadian “natural health products” to treat lice, too). No recommendations are made in favour of any “natural” or herbal products.

With respect to non-chemical treatments (manual removal of nits), the AAP isn’t that enthusiastic. It cites one study suggesting manual removal isn’t as effective as chemicals, though it notes that wet-combing seems superior to dry-combing. Not surprisingly, it isn’t that enthusiastic about electronic devices to help with manual removal (Quantum MagiComb, anyone?) noting there’s a lack of data showing they’re effective. As I pointed out previously, the manual removal approach does work and I endorse it for parents that refuse to use chemical approaches. But I caution them the risk of failure is higher, there is no room for error, and there is good evidence to demonstrate the chemical treatments are safe and effective when used properly.

The impetus for my initial post last year on head lice were some questionable recommendations from a local school which summarized (in part) the recommendations from the Toronto District School Board. The AAP report provides good information on control measures for schools, and general information on treatment measures. I won’t go into them in detail, but recommend you consult them if you’re concerned about how schools manage lice outbreaks. Here’s a few highlights, and I hope the TDSB reviews the AAP’s evidence, and ensures Toronto public schools use evidence-based practices.

  • Lice can’t hop or fly, but the static electricity from brushing hair can eject lice more than 1 metre. Despite this, indirect spread (i.e., student-to-student), while possible, is still unlikely. Lice on healthy heads are unlikely to leave: A study of 118 classroom floors found no head lice despite the presence of 14,000 lice on the head of 466 children. So what’s the takeaway? Focus control on reducing the number of lice on the head, and lessen the risk of head-to-head contact.
  • The standard for diagnosing head lice is finding head lice – not nits (eggs). Nits more than 1cm up on the follicle are unlikely to be viable – so they do not mean there’s a lice infection.
  • Never treat unless there is a clear diagnosis of head lice. There’s no reason to treat the entire family if only the kids have lice.
  • Only items that have been in contact with the head of the person with infestation in the 24-48 hours before treatment should be considered for cleaning, as louse survival >48 hours is unlikely. Pediculoside sprays are not necessary.
  • School screening for nits or lice isn’t an accurate way of predicting if children are, or will become, infested. Screening in schools has not been demonstrated to have a significant effect on the incidence of head lice. “Because of the lack of evidence of efficacy, routine classroom or school-wide screening should be discouraged, ” says the report.
  • Only a fraction of children with nits (eggs) actually have concomitant infections, or go on to develop infections. Excluding children from school who have nits alone is unnecessary, and could result in unnecessary treatments being administered.
  • A child with an active infestation has likely been colonized for a month or more – therefore sending a child home immediately from school is unnecessary. The parents should be contacted or a note sent home, asking the child to be treated. There are mixed reports about the effectiveness about “alert letters” sent home with other children in the class.
  • Children should not be restricted from school because of lice. No nit policies in schools are inappropriate, not based on objective evidence, and should be abandoned.

So, as the Globe said, is it true that chemical treatments may not work? The bottom line is that chemical treatments are safe and effective, but lice aren’t as easy to treat as perhaps we’d like. What seems to be far more resistant to treatment are the beliefs and stereotypes about head lice that stigmatize children, disrupt families, and lead to unnecessary treatments.


Frankowski, B., & Bocchini, J. (2010). Head Lice PEDIATRICS, 126 (2), 392-403 DOI: 10.1542/peds.2010-1308

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