Scientists say that lice are becoming immune to common treatments, a worry for parents as children will soon be back to school. A high level of resistance to some of the most popular treatments has been developed by nits.

Lice have developed resistance to over-the counter treatments in at least 25 American states. The treatments are still recommended by doctors and schools.

Doctor Kyong Yoon, of Southern Illinois University, said, “We are the first group to collect lice samples from a large number of populations across the United States. What we found was that 104 out of the 109 lice populations we tested had high levels of gene mutations, which have been linked to resistance to pyrethroids”.

Pyrethroids belong to a family of insecticides meant for use indoors and outdoors to control mosquitoes and other insects.

Permethrin, the active ingredient in some of the most common lice treatments sold over the counter, is present in them. Dr. Yoon said permethrin products were made available for sale in the US in the early ’90s.

The ability of lice to become more resistant to pyrethroid has only increased over the past many years, said Dr. Yoon. Israel first reported the development of the momentum toward widespread pyrethroid-resistant lice in the late 1990s.

Dr. Yoon said that he was working on an insecticide metabolism in a potato beetle when he was asked by his mentor John Clark to look into the resurgence of head lice. When he asked which country he should look for, he was left surprised as his mentor said the US.