A new study that suggests ‘super-lice,’ or lice that are resistant to over-the-counter medication, have become more widespread in the United States.

The research, published in the March edition of the Journal of Medical Entomology, found that lice resistant to common treatments containing pyrethroids have reached 48 U.S. states, up from an estimated 25 states reported by another group in February. For over-the-counter lice medication, the Centers for Disease Control and Prevention recommends taking products like A-200, Pronto, R&C, Rid, Triple X and Licide, all of which contain pyrethrins combined with piperonyl butoxide.

The study, which is making its media rounds now at the start of the school year, concluded that head lice collected at 138 sites across the country had a resistance aelle frequency (RAF) of 98 percent and that these lice contained a resistant trait called knockdown resistance (kdr), indicating their resistance to pyrethroids.

“I suggest parents who have infested children in their home talk to doctors first before using over-the-counter pyrethroid-, pyrethrins-containing pediculicidal products,” study author Dr. Kyong Yoon, an assistant biological sciences professor at Southern Illinois University Edwardsville, told FoxNews.com in an email.

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In addition to consulting with pediatricians and pediatric dermatologists, Yoon recommended considering prescription-based pediculicides to treat lice.

“Kdr lice in the U.S. were first reported in 2000, and now we know that lice with this resistance trait are everywhere in the U.S.,” he said.  “We need to implement efficient resistance management strategies to suppress or prevent development of resistance to these new chemicals.”