Lice Are Becoming Resistant to Treatment

A mother checks her child's hair for lice. New research found that lice in 25 states in the U.S. are resistant to many of the treatments typically used to eliminate the insects and their eggs. Johan Lenell/Alamy

The very thought of head lice makes most people scratch their head in psychosomatic agony. These vermin are a persistent nuisance throughout the school year, but the one saving grace for families has typically been that over-the-counter treatments effectively kill these itty-bitty bugs. Lice are exceedingly common—according to the U.S. Centers for Disease Control and Prevention, approximately 6 million to 12 million infestations occur each year in the country among children 3 to 11—but also very easy to treat.

Unfortunately, nitpicking parents should brace themselves for some disheartening news (and grab a few extra fine-toothed metal combs).

New research released just in time for the start of the academic year finds lice in 25 states in the U.S. are now resistant to some of the treatments typically used to eradicate the live pests and their eggs. Scientists this week presented their findings at the 250th National Meeting and Exposition of the American Chemical Society. They found that 104 in 109 lice population samples tested had genetic mutations that make the pests resistant to pyrethroids, the active chemical in many shampoos and other treatments that kill the bugs. Pyrethroids are used for indoor and outdoor pest control, including mosquitoes. Most of the over-the-counter products for lice removal contain either pyrethrin (sold widely under the brand name Rid) or permethrin (includes the brand name Nix).

The researchers say while this may be news to consumers, the scientific community has known for years about the emerging problem. Kyong Yoon, a scientist at the Southern Illinois University in Edwardsville, was researching insecticide resistance in potato beetles when his mentor suggested he investigate the resurgence of lice in the U.S.

Yoon tested lice samples from local schools in Illinois for a group of three genetic mutations known as knock-down resistance (KDR). These mutations were discovered in houseflies in the late 1970s, after farmers began using pyrethroids instead of DDT.

After evaluating these samples, Yoon found a large majority had the trio of genetic mutations, which makes them resistant to the chemical. He next expanded his evaluation and began collecting lice from 30 states in the U.S. He found the bugs that came from 25 states had genetic mutations that cause pyrethroid-resistance. All lice samples from California, Texas, Florida and Maine had all three mutations, while those from New York, New Jersey, New Mexico and Oregon had one, two or three mutations. Families in Michigan can breathe a sigh of relief. Out of all the states included in the analysis, Michigan was the only one where lice were not found to have KDR mutations.

There are chemicals besides pyrethroids that are effective for eliminating a lice infestation, but these treatments may require a prescription. Some, such as spinosad and malathion, are classified by the U.S. Environmental Protection Agency as carcinogenic or toxic to the central nervous system. A number of other methods have been found to work, such as working a metal nitpicking comb through hair that's coated in coconut or olive oil—the oil effectively suffocates the bugs. For best results, experts suggest coating hair in oil and sealing it with a shower cap overnight.