Nits, or head lice, are every parent's nightmare.
And it's about to get worse with head lice developing immunity to the over-the-counter products used to treat them, according to new research.
Normally, head lice are treated with chemicals called insecticides and a fine tooth comb, to scrape out the dead lice and eggs.
A study published in the Journal of Economic Entomology took 140 head lice samples from people in 48 American states, and over 95 per cent of the lice had genetic markers for resistance to chemical treatments.
"We've suspected for a long time that head lice are becoming resistant to these commonly used insecticides, because we continually hear about people experiencing treatment failures," medical entomologist Dr Cameron Webb, from the University of Sydney, told news.com.au.
"It's no surprise given the anxiety many parents have about head lice. We're quick to use
these treatments to control the infestation and the side effect of that is we're increasing the chances that insecticide resistance will develop," Dr Webb said.
Chemical head lice treatments usually don't kill all of the head lice, so the survivors often develop an immunity to the insecticide.
"Their offspring are resistant to insecticide as well," Dr Webb said, "so it's almost like we're creating super lice, because we're killing all the weak head lice and the strongest ones are surviving."
The best way to treat head lice is by using a cheap conditioner and a fine tooth comb.
"Massage the conditioner in the hair and that stuns the lice, so they can't crawl around anymore. Use a comb and remove the lice from the hair. Repeat that process one week later to catch the lice that have hatched from any leftover eggs," he said.
Dr Webb says parents should be aware that head lice don't pose a big health risk to children.
"The far greater concern is the stress and anxiety it causes to parents and carers because of the social stigma," he said.
"If we had a more relaxed attitude to being able to control them, and the patience and perseverance to use combs, then we'd be in a much better place."