‘Super’ Head Lice Develop Defense Against Common Permethrin Treatment: Confirmed In 25 States

A new report presented by the American Chemical Society at the 250th National Meeting & Exposition of the ACS suggests that a new type of “super” head lice in 25 states has developed resistance against popular over-the-counter treatments.

The release of the report coincides with the start of a new school year, something that often involves the exposure to head lice among students.

The most common treatment for head lice involves the use of pyrethroids, a class of insecticides that is used both indoors and out to combat insects like mosquitoes, black flies, and head lice. The pyrethroid ingredient permethrin is found in most over-the-counter lice remedies.

Kyong Yoon, a Southern Illinois University Ph.D., spoke about the head lice findings.

“We are the first group to collect lice samples from a large number of populations across the U.S. What we found was that 104 out of the 109 lice populations we tested had high levels of gene mutations, which have been linked to resistance to pyrethroids.”

Noteworthy is that Dr. Yoon and researchers have only be able to collect samples from 30 states. Of these, 25 contained populations of head lice completely resistant to pyrethroids, four contained partially resistant lice, and one state’s lice had no resistance.

Head lice that have been exposed to pyrethroids develop three known mutations that lead to a population of lice becoming resistant. Twenty-five states are home to head lice that have developed all three mutations. Samples of head lice from New York, New Jersey, New Mexico, and Oregon each showed one, two, or three mutations.

Michigan is the only state whose lice population has been unaffected — and that can still be effectively treated with pyrethroids. The reason for the lack of mutations among Michigan head lice is still being studied. It has been suggested that Michigan lice and others with fewer mutations have been accidentally imported from overseas where lice medications like pyrethroids are not in use.

Dr. Yoon goes on to explain that the solution to the resistant “super” lice is to use remedies that use different chemicals, which are only available by prescription. This strategy is not without hazards.

Alternative head lice treatments include ivermectin-containing Sklice and spinosad-containing Natroba. The use of each is seen as carrying more risk than permethrin use. Furthermore, Dr. Yoon warns that lice may develop resistance again in the future.

“If you use a chemical over and over, these little creatures will eventually develop resistance. So we have to think before we use a treatment. The good news is head lice don’t carry disease. They’re more a nuisance than anything else.”

[Lice Photo by Sean Gallup/Getty Images]