Clinical evidence of lice resistance to over-the-counter products

J Cutan Med Surg. 2000 Oct;4(4):199-201. doi: 10.1177/120347540000400405.


Background: Over-the-counter insecticidal solutions continue to be the mainstream treatment for most cases of head lice. Recorded insecticidal activity 15 years ago was at 100%, with ovicidal kill at 80%. Recently scattered accounts of possible resistance have surfaced.

Objective: This article is to document the general consensus that head lice are becoming resistant to standard over-the-counter therapies.

Methods: Direct testing of lethality of adult lice with permethrin and pyrethroid was assessed.

Results: Present over-the-counter products proved to be successful in only 9 of 32 head lice tested (28% insecticidal activity).

Conclusions: Our series of cases further documents that over-the-counter head lice preparations no longer achieve high levels of insecticidal activity, suggesting increased resistance to these insecticides.

MeSH terms

  • Animals
  • Child
  • Drug Combinations
  • Drug Resistance, Microbial
  • Humans
  • Insecticides / pharmacology
  • Insecticides / therapeutic use*
  • Lice Infestations / drug therapy*
  • Pediculus* / drug effects
  • Permethrin
  • Piperonyl Butoxide / pharmacology
  • Piperonyl Butoxide / therapeutic use*
  • Pyrethrins / pharmacology
  • Pyrethrins / therapeutic use*
  • Scalp Dermatoses / drug therapy*
  • Treatment Failure


  • Drug Combinations
  • Insecticides
  • Pyrethrins
  • RID
  • Permethrin
  • Piperonyl Butoxide