Researchers have warned few years ago, head lice in the U.S. and all over the world are developing immunity against strong insecticides used in prescribed shampoos and counter products. It takes four to five years for the parasites to adapt a new product, in spite of claims to the contrary by the manufacturers, noted Shirley C. Gordon, an associate professor at Florida Atlantic University who studies relentless head lice.

Health officials have kept on recommending the products, because drugs like the permethrin, pyrethrin, lindane and the prescription malathion still effective in some people.

But the nation’s school nurses say it’s obvious to them that families facing problem due to the bugs are annoyed with the product failures. “I had a mom drag her child into my office on the first day of school,” said Jill Burgin, a registered nurse. “She had been battling it throughout the summer and wanted advice on where to go from there.”

In the estimation of federal Centers for Disease Control and Prevention, between 6 to 12 million children aged 3 to 11 are infested each year.

Under-diagnosis of lice is common among parents and health workers who usually miss the indications of the tan-colored lice and their small, opalescent eggs, called nits. But over-diagnosis also creates problem when it participate in hysteria that keeps healthy children away from school. “Real as well as imagined infestations are over-treated, often multiple times,” Pollack said.

Several products are awaiting approval by the FDA in coming months that claimed to work in 30 minutes instead of up to 12 hours. Gordon said she is also interested in pending FDA approval of a product called the Louse Buster. It uses a high-volume air dryer that uses hot air to dehydrate lice.

Until modern and effective treatments are found, parents will have to experiment old fashioned medications and treatments, such as removing nits with a fine-toothed comb.