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As the summer holidays come to a close, parents are being warned that nits are increasingly resistant to many of the most popular treatments.
Scientists of Southern Illinois University studied samples of lice and discovered many are becoming immune to popular lice treatments, leaving parents struggling to battle nits in their children’s hair.
The study revealed that lice have developed ‘high-levels resistance’ to many treatments, which could leave parents both frustrated at being unable to find a solution and children missing days of school.
Dr 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."
Head lice are very common in children at primary school and spread by close head-to-head contact. Causing itching and inflammation as they feed on blood from the scalp they are living on.
Scientists studied 109 different lice populations across more than 25 American states and discovered that almost 100 per cent of those studied has developed resistance to over-the-counter chemical treatments recommended by doctors and schools.
Pyrethroids are derived from the chemical family, insecticides and are commonly used both indoors and outdoors to control the levels of both mosquitos and other insects. Permethrin is an active ingredient found in lice treatment products sold over-the-counter.
Dr Yoon previously studied genetic mutations, commonly known as ‘knock-down-resistance’ (kdr) in house flies during the 70s when farmers began using pyrethroids as insecticides.
When studying head lice, he found they had kdr mutations, affecting the nervous system and desensitising them to pyrethroids.
In his most recent study, Dr Yoon collected lice samples from 30 states and found samples from 25 states contained genetic mutations commonly associated with kdr, resulting in them being most resistant to pyrethroids.
The findings were presented at the 250th national meeting and exposition of the American Chemical Society.
Despite the findings, lice are still susceptible to other chemicals, many of which are available on prescriptions. Dr Yoon added: “If you use a chemical over and over, these little creatures will eventually develop resistance. So we have to think before we use a treatment. The good news is head lice don't carry disease. They're more a nuisance than anything else."
Common non over-the-counter or prescription remedies for head lice include: tea tree oil shampoo, and daily conditioning and combing with a fine lice comb.