Lice shampoos ineffective: researchers

LOS ANGELES - Shampoos created to combat head lice aren't working because of overuse, according to California researchers.

"The lice are becoming resistant and resistant lice are taking over," says John Clark of the University of California.

One to 10 percent schoolkids have head lice at any one time

Clark's team of researchers is trying to find out why the lice don't die when doused and scrubbed with pesticide-based shampoo.

Thousands of school children are afflicted with the itchy pests every year. The Canadian Pediatric Society estimates one to 10 percent of all schoolchildren are infested at any time.

There are five products available in Canada for treating head lice.

Clark says the active ingredient in the shampoos attack the insect's central nervous system and causes them to suffocate. The poison acts in the same way as DDT — a pesticide widely used to kill lice before being banned in 1973.

He says the lice began developing immunity to DDT and when the pesticide-based shampoos were introduced in the 1980s, they helped the resistant strain of lice evolve.

"We started hearing about resistance in 1994," says Clark. "I would say within five to 10 years... they won't be effective at all."

Researchers believe over-use of the shampoos has created the situation.

"When people get lice, they want to get rid of them as fast as possible and that leads to misuse of products designed to kill them," says Steven Shuman of the California Department of Public Health.

Deborah Altschuler, head of the National Pediculosis Association which advocates against the misuse of pesticidal lice treatments, says she has spoken to many frustrated parents.

"They've spent all this money on products that didn't do anything, and their kids still have lice."

Altschuler says picking lice and their eggs off a scalp is the best way to get rid of them.

Clark believes there's an alternative. He says the development of new products that mix different active ingredients could be the answer. By mixing compounds that kill lice differently, it would take the insects longer to develop their resistance to multiple products as opposed to a single one.

"It's going to have to be done through very controlled prescription use of pesticides," warns Clark. "When these things are sold over-the-counter, they're not used properly."

Clark's team studied the lice by creating an artificial scalp — tubes with tufts of human hair and a thin plastic membrane spread over the bottom of the tube. The tube is placed in a container of blood for the lice to feed on.

Researchers will continue to study how lice spread so quickly.