Source: Consumer Reports, September 2015

Many parents, desperate to get rid of lice crawling around in their child’s hair, will dash out to the pharmacy to buy Nix or Rid, the most widely sold lice-control products in an estimated $130 million over-the-counter market.

There’s a reason those chemical products are so popular. The American Academy of Pediatrics and the Centers for Disease Control and Prevention on their websites recommend using those pesticides, as well as even stronger prescription-only products, to get rid of the nasty insects. But Consumer Reports says you should physically remove them instead.

“There’s no reason for parents to douse their children’s heads in chemicals,” says Urvashi Rangan, Ph.D., director of consumer safety and sustainability for Consumer Reports. “Physically removing lice, while it seems daunting, is safest for your child’s head.”

The over-the-counter products are losing their fight against lice because studies suggest that most of the bugs in the U.S. have evolved to become genetically resistant to the insecticides found in those products. That includes pyrethrum in shampoos such as Rid and the permethrin in creme rinses such as Nix. Pyrethrum is a naturally occurring pyrethroid extract from the chrysanthemum flower, and permethrin is a synthetic form of that drug. Products with those ingredients have been available to consumers for decades.

A study published in the March 2014 issue of the Journal of Medical Entomology found that 99 percent of the head lice collected by school nurses and professional lice combers in 12 states and three Canadian provinces were genetically resistant to permethrin. “It’s not surprising that we are seeing a resistance to these products,” Rangan says. “That’s what happens with insecticides and pests over time.”

And despite the label claims, pyrethrin- and pyrethroid-based products have only a marginal ability to kill the eggs that remain attached to the hair shaft after treatment. “They can’t be relied on to kill all lice eggs,” says Michael Hansen, Ph.D., a senior scientist at Consumer Reports. When the makers of Nix were asked for the evidence to support the claim that Nix “kills lice and their eggs,” a lawyer for the company said its labeling is scrutinized by the Food and Drug Administration, but the content behind it is considered “proprietary and confidential.”

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