A recent review on head lice treatments available in the United States described a marked decline in the effectiveness of permethrin/synergized pyrethrins (collectively pyrethroids), likely due to resistance arising from widespread and indiscriminate use over 30 years.

The review also noted that the potential toxicity of lindane, and the availability of safer and more effective alternatives, should limit its use. Prescription products that are safe and effective include malathion, benzyl alcohol, spinosad, and topical ivermectin.

Home remedies such as petroleum jelly, mayonnaise, and essential oils, have not been demonstrated as safe or effective and may cause adverse reactions.

"Our findings indicate that over-the-counter treatments for head louse infestations are no longer likely to be effective," said Dr. Terri Meinking, co-author of the Pediatric Dermatology study. "The lesson we should learn is that those products that do remain effective, which are available by prescription, should be used judiciously so that they do not suffer the fate that has befallen the pyrethroids," added lead author Dr. Ellen Koch.