Daily News Archive
From February 26, 2002

The Persistence of Head Lice

It is estimated that there are 6 million to 12 million cases of head lice a year, according to a New York Times article. Research suggests that lice and their eggs are increasingly resistant to the over-the counter shampoos recommended by most pediatricians and school administrators, making lice more and more difficult to kill.

Over the last 10 years, researchers from the Czech Republic, England, France and Israel have pointed to increased resistance to permethrin, the active ingredient in anti-lice shampoos most often recommended by physicians. In a 1999 study published in The Archives of Pediatric and Adolescent, Dr. Richard Pollack, an instructor in the department of immunology and infectious diseases at the Harvard School of Public Health, and his colleagues found that head lice collected from two sites in the U.S. were not killed by permethrin, even when exposed to progressively higher doses. In contrast, lice collected from children in Borneo, where permethrin is rarely used, were killed. A study in the current issue of The Archives of Dermatology is part of a growing body of evidence showing that resistance to over-the-counter live treatments "is reaching epidemic levels in the U.S."

Teri L. Meinking, a research assistant professor at the University of Miami School of Medicine and well-known lice expert, recently looked at two different prescription medications and several over-the-counter formulas to find out whether lice had become resistant to them. Her study, published in February in The Archives of Dermatology, found that Nix killed 3 to 5 percent of lice after 10 minutes (the recommended time) and 8 to 10 percent after 20 minutes. RID killed 7 percent in 10 minutes. The prescription Ovide, containing the organophosphate malathion, killed 88 percent in 10 minutes, but is also a nerve poison.

"Lice have genetically mutated to survive the medication," said Professor Meinking. "They can walk around on permethrin and not be fazed. It's clear these products don't work."

For more information about head lice control, permethrin or malathion, see our factsheets online or contact Beyond Pesticides.

To view the full article, see: http://www.nytimes.com/2002/02/26/health/children/26LICE.html